METAL ION COMPLEXING PROPERTIES OF THE …dl.uncw.edu/Etd/2010-1/merrilld/daniellemerrill.pdfDiagram of the PUREX process for the separation of uranium and plutonium from fission products

METAL ION COMPLEXING PROPERTIES OF THE HIGHLY PREORGANIZED

TETRADENTATE LIGAND 1,10-PHENANTHROLINE-2,9-DICARBOXAMIDE

Danielle Merrill

A Thesis Submitted to the

University of North Carolina Wilmington in Partial Fulfillment

of the Requirements for the Degree of

Master of Science

Department of Chemistry and Biochemistry

University of North Carolina Wilmington

2010

Approved by

Advisory Committee

Jeremy B. Morgan John A. Tyrell

Robert D. Hancock

Chair

Accepted by

_________________________________

Dean, Graduate School

ii

TABLE OF CONTENTS

ABSTRACT .........................................................................................................................v

ACKNOWLEDGMENTS ................................................................................................. vi

DEDICATION .................................................................................................................. vii

LIST OF TABLES ........................................................................................................... viii

LIST OF FIGURES ........................................................................................................... xi

INTRODUCTION ...............................................................................................................1

Ligands in Nuclear Waste Industry.................................................................................1

1,10-Phenanthroline-2,9-dicarboxamide.........................................................................5

Chelate Ring Size ............................................................................................................7

Hard and Soft Acid-Base (HSAB) Theory .....................................................................8

Donor Atoms .................................................................................................................11

Preorganization .............................................................................................................13

METHODS AND MATERIALS .......................................................................................15

General and Chemicals .................................................................................................15

Synthesis of PDAM ......................................................................................................15

UV/Vis Spectrophotometry ..........................................................................................19

iii

Fluorescence ................................................................................................................ 24

Degradation Experiment ................................................................................................27

Molecular Mechanics Calculations ...............................................................................27

RESULTS AND DISCUSSION ........................................................................................28

Synthesis of PDAM ......................................................................................................28

Protonation Constant .....................................................................................................40

Log K1 Results for Metal Ions Studied .........................................................................43

Nickel Results ...............................................................................................................46

Zinc Results ..................................................................................................................50

Scandium Results ..........................................................................................................55

Copper Results ..............................................................................................................59

Indium Results ..............................................................................................................63

Uranyl Results ...............................................................................................................67

Yttrium Results .............................................................................................................71

Thorium Results ............................................................................................................75

Cadmium Results ..........................................................................................................79

Calcium Results ............................................................................................................86

iv

Bismuth Results ............................................................................................................90

Lead Results ..................................................................................................................94

Lanthanide Series Results ............................................................................................ 97

Fluorescence Results ...................................................................................................126

PDAM Degradation Experiment .................................................................................136

Molecular Mechanics Calculations .............................................................................138

CONCLUSIONS..............................................................................................................141

REFERENCES ................................................................................................................143

v

ABSTRACT

The highly preorganized ligand 2,9-diamide-1,10-phenanthroline (PDAM) has

promising uses in nuclear chemistry. By utilizing key ligand design techniques, PDAM

will allow the formation of very stable complexes with the minor actinide metal ions, in

particular americium and curium which are produced as a by-product in nuclear energy

reactors. By reprocessing this spent nuclear fuel it addresses two major concerns. The

long-lived radioactivity of the residue is greatly reduced as well as allowing purified

235U and

239Pu to be used as reactor fuel. The qualities of PDAM demonstrate its

capability of being a desired ligand for reprocessing since it possesses properties such

as a rigid backbone which allows it to have a high degree of preorganization.

Additionally, PDAM possesses N-donor and O-donor atoms which enhance the

selectivity of the desired actinide metals. The weak proton basicity of PDAM may also

be an important factor in its use as a solvent extractant from acidic solutions. The

ligand PDAM was synthesized and subjected to purity verification for studies in

formation constants with various aqueous metal-ions. Formation constants were

determined from UV/Vis spectrophotometry detection to establish the protonation and

stability constants of the free ligands with metal ions of interest such as the Ln(III) ions

(excluding Pm(III)), as well as several different metal ions of varying ionic charges and

radii. PDAM was found to be highly selective for bismuth and indium with a log

K1=9.44 and log K1=9.43 respectively. The log K1 values for the Ln(III) ions show only

a small variation from La(III) to Lu(III) with both ions containing a log K1 = 3.80. The

best-fit size of metal ion for coordination with PDAM was analyzed using molecular

mechanics calculations.

vi

ACKNOWLEDGEMENTS

I would like to thank my advisor Dr. Robert Hancock for all his help and

support in my academic career in addition to furthering my knowledge in the vast field

of inorganic chemistry. I would also like to thank my committee members Dr. John

Tyrell and Dr. Jeremy Morgan for their help in my endeavors.

Finally, I would like to thank my chemistry friends (Neil Williams, Amy Mroz,

Jennifer Wilent, Natalie Mitchell), my family and my wonderful boyfriend. Without

their support and encouragement through the hard times I would never be able to make

it to where I am today. Thank you all for the awesome memories!

vii

DEDICATION

I would like to dedicate my thesis to the most epic band of all time MUSE.

Thank you, Matt Bellamy, for your amazing vocals and guitar riffs to get me through

each day.

viii

LIST OF TABLES

Table Page

1. Classification of hard and soft acids and bases by HSAB principle .........................10

2. Formation constants for ammonia complexes in aqueous solution for a selection

of metal ions. .............................................................................................................12

3. Summary of prepared metal solutions ......................................................................20

4. Summary of prepared competition reaction solutions with PDAM all diluted

from1.0*10-3

stock solutions .....................................................................................21

5. Summary of the preparation of fluorescence solutions.............................................25

6. List of log K1 for PDAM with various metal ions in order of ionic radii (Å) ........44

7. Solutions and standard deviation for each parameter used by SOLVER module

of EXCEL in the determination of log K1 of PDAM-Ni complex. .........................49


of EXCEL in the determination of log K1 of PDAM-Zn complex. .........................54


of EXCEL in the determination of log K1 of PDAM-Sc complex. .........................58


of EXCEL in the determination of log K1 of PDAM-Cu complex. .........................62


of EXCEL in the determination of log K1 of PDAM:TETREN:In 1:1:1. ...............66


of EXCEL in the determination of log K1 of PDAM-UO2 complex. ......................70


of EXCEL in the determination of log K1 of PDAM-Y complex. ...........................74


of EXCEL in the determination of log K1 of PDAM-Th complex. .........................78


of EXCEL in the determination of log K1 of PDAM:EDTA:Cd 1:1:1 complex.. ...84

ix


of EXCEL in the determination of log K1 of PDAM:TETREN:Cd 1:1:1

complex.. ..................................................................................................................84


of EXCEL in the determination of log K1 of PDAM-Ca complex. .........................89


of EXCEL in the determination of log K1 of PDAM:TETREN:Bi 1:1:1

complex. ....................................................................................................................92


of EXCEL in the determination of log K1 of PDAM:TETREN:Pb 1:1:1

complex. ...................................................................................................................97

20. Protonation and formation constants for the lanthanide(III) series with PDAM

determined in 0.1 M NaClO4 at 25 ºC. (L = PDAM in given equilibria) ..............103


of EXCEL in the determination of log K1 of PDAM-La complex. .......................119


of EXCEL in the determination of log K1 of PDAM-Ce complex. .......................119


of EXCEL in the determination of log K1 of PDAM-Pr complex. ........................119


of EXCEL in the determination of log K1 of PDAM-Nd complex. .......................120


of EXCEL in the determination of log K1 of PDAM-Sm complex. ......................120


of EXCEL in the determination of log K1 of PDAM-Eu complex. .......................121


of EXCEL in the determination of log K1 of PDAM-Gd complex. .......................121


of EXCEL in the determination of log K1 of PDAM-Tb complex. .......................122

x


of EXCEL in the determination of log K1 of PDAM-Dy complex. .......................122


of EXCEL in the determination of log K1 of PDAM-Ho complex.........................123


of EXCEL in the determination of log K1 of PDAM-Er complex ..........................123


of EXCEL in the determination of log K1 of PDAM-Tm complex ........................124


of EXCEL in the determination of log K1 of PDAM-Yb complex.........................124


of EXCEL in the determination of log K1 of PDAM-Lu complex .........................125

xi

LIST OF FIGURES

Figure Page

1. Trans-uranium elements formed in a nuclear reactor .................................................2

2. Diagram of the PUREX process for the separation of uranium and plutonium

from fission products ..................................................................................................3

3. Structures of BTP, TPEN, di-phenyl-phen, and TPTZ ...............................................5

4. Summarization of the ideal characteristics of the PDAM complex ............................6

5. Classification of metal according to HSAB principle and illustration of periodic

table trend....................................................................................................................9

6. Structure of L1, BTP, and TBP .................................................................................11

7. Structures of PDA, PDAM, DPP, 1,10-phen and PDALC .......................................13

8. Chemical structure of QUATERPY compared to the chemical structure of

PDAM to illustrate preorganization ..........................................................................14

9. Schematic of the synthesis of PDAM. .....................................................................18

10. Diagram of a flow cell apparatus used in the titration experiments .........................23

11. Diagram of a flow cell apparatus used in fluorescence experiments ........................26

12. M-N and M-O bond lengths calculated through molecular mechanics

calculations. ..............................................................................................................27

13. IR-spectra of PDALD in KBr pellet .........................................................................29

14. NMR-spectra of PDALD in DMSO-d5 .....................................................................30

15. IR spectra of PDA in KBr pellet ...............................................................................32

16. NMR spectra of PDA in DMSO-d5 ..........................................................................33

17. IR-spectra of PBE in KBr pellet ...............................................................................35

18. NMR-spectra of PBE in DMSO-d5 ...........................................................................36

19. IR-spectra of PDAM in KBr pellet ...........................................................................38

xii

20. NMR-spectra of PDAM in DMSO-d5.......................................................................39

21. UV-Vis absorbance spectrum of the titration of PDAM at 2.00x10-5

M ...................41

22. Protonation equilibrium for 2,9-diamide-1,10-phenanthroline (PDAM) .................42

23. UV/Vis spectra of PDAM (2x10-5

M) and Ni(ClO4)2 (0.10 M) with 0.1 M

NaClO4 present held at a pH 5.37 .............................................................................47

24. Plot of absorbance (data points) and theoretical absorbance (lines) versus

log[Ni] for titration of PDAM and Ni(ClO4)2. ..........................................................48


M) and Zn (0.3333 M) with 0.1 M NaClO4

present. Initial pH at 5.31 ..........................................................................................51


M) and Zn (0.3333 M) with 0.1 M NaClO4

present. Initial at pH 4.19 ..........................................................................................52


log[Zn] for titration of PDAM and Zn(ClO4)2. .........................................................53


M) and Sc(0.003361 M) with 0.1 M NaClO4

present. Initial pH at 2.14. .........................................................................................56


log[Sc] for titration of PDAM and Sc(ClO4)3. ..........................................................57

30. UV/Vis spectra of PDAM:TETREN:In (2x10-5

M) with 0.1 M NaClO4 present.

Initial pH at 2.07 to a final pH of 7.31. .....................................................................60

31. Plot of absorbance (data points) and theoretical absorbance (lines) versus pH for

titration of PDAM:TETREN:In (2x10-5

M). ..............................................................61


M) and UO2(0.003333 M) with 0.1 M

NaClO4 present. Initial pH at 2.11. ...........................................................................64


log[UO2] for titration of PDAM and UO2(NO3)2. ....................................................65


M) and Cu(0.003522 M) with 0.1 M NaClO4



log[Cu] for titration of PDAM and Cu(ClO4)2 ........................................................69

xiii


M) and Y(0.003333 M) with 0.1 M NaClO4


37. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Y]

for titration of PDAM and Y(NO3)3..........................................................................73


M) and Th(0.003488 M) with 0.1 M NaClO4



log[Th] for titration of PDAM and Th(NO3)4. ..........................................................77


M) and Cd(0.003230 M) with 0.1 M NaClO4


41. UV/Vis spectra of PDAM:Cd(ClO4)3:EDTA 1:1:1 (2x10-5

M) and 0.1 M

NaClO4 present. Initial at pH 2.20. ...........................................................................81

42. UV/Vis spectra of PDAM:Cd(ClO4)3:TETREN 1:1:1 (2x10-5

M) and 0.1 M

NaClO4 present. Initial at pH 2.44 to a final pH of 9.49. ..........................................82

43. Plot of corrected absorbance (data points) and theoretical absorbance (lines)

versus pH for titration of 1:1:1 PDAM:Cd(ClO4)2:EDTA. ......................................83

44. Plot of corrected absorbance (data points) and theoretical absorbance (lines)

versus pH for titration of 1:1:1 PDAM:Cd(ClO4)2:TETREN. ..................................84


M) and Ca(1.0 M) with 0.1 M NaClO4

present. Initial pH 5.37..............................................................................................87


log[Ca] for titration of PDAM and Ca(ClO4)2. .........................................................88

47. UV/Vis spectra of PDAM:TETREN:Bi (2x10-5

M) with 0.1 M NaClO4 present.

Initial pH at 2.10 to a final pH of 7.11. .....................................................................91


pH for titration of PDAM:TETREN:Bi (2x10-5

M). ..................................................92

49. UV/Vis spectra of PDAM :TETREN:Pb 1:1:1 (2x10-5

M) with 0.1 M NaClO4

present. Initial pH at 2.27 to final pH of 8.11. ..........................................................95


pH for titration of PDAM:TETREN:Pb 1:1:1 ..........................................................96

xiv


M) and Ce(0.003333 M) with 0.1 M NaClO4

present. Note the sharp band at 250 nm. ...................................................................99

52. Plot of change in log K1 for various ligands comparing the La(III) complex for

Ln(III) ions as a function of the number of f-electrons ..........................................100

53. Comparison of ionic radii for the Ln(III) ions in angstroms. .................................101


M) and La(0.003333M) with 0.1 M NaClO4

present. Initial pH at 5.46 ........................................................................................104


M) and Ce(0.003333 M) with 0.1 M NaClO4



M) and Pr(0.003402 M) with 0.1 M NaClO4



M) and Nd(0.003385 M) with 0.1 M NaClO4

present. Initial pH at 2.12. .......................................................................................106


M) and Sm(0.003505 M) with 0.1 M NaClO4



M) and Eu(0.003360 M) with 0.1 M NaClO4

present. Initial pH at 2.17 .......................................................................................107


M) and Gd (0.003333M) with 0.1 M NaClO4



M) and Tb(0.003557 M) with 0.1 M NaClO4



M) and Dy(0.003557 M) with 0.1 M NaClO4



M) and Ho(0.003271 M) with 0.1 M NaClO4



M) and Er(0.003354 M) with 0.1 M NaClO4



M) and Tm(0.003343 M) with 0.1 M NaClO4


xv


M) and Yb(0.003333 M) with 0.1 M NaClO4



M) and Lu (0.003333M) with 0.1 M NaClO4



log[La] for titration of PDAM and La(ClO4)3. .......................................................112


log[Ce] for titration of PDAM and Ce(ClO4)4. .......................................................112


log[Pr] for titration of PDAM and Pr(ClO4)3. .........................................................113


log[Nd] for titration of PDAM and Nd(ClO4)3. ......................................................113


log[Sm] for titration of PDAM and Sm(ClO4)3. .....................................................114


log[Eu] for titration of PDAM and Eu(OSO2CF3)3. ...............................................114


log[Gd] for titration of PDAM and Gd(ClO4) 3. .....................................................115


log[Tb] for titration of PDAM and Tb(ClO4)3. .......................................................115


log[Dy] for titration of PDAM and Dy(ClO4)3. ......................................................116


log[Ho] for titration of PDAM and Ho(ClO4)3. ......................................................116


log[Er] for titration of PDAM and Er(ClO4)3. ........................................................117


log[Tm] for titration of PDAM and Tm(CF3SO3)3. ................................................117


log[Yb] for titration of PDAM and Yb(NO3)3. .......................................................118

xvi


log[Lu] for titration of PDAM and Lu(ClO4)3. .......................................................118

82. Resonance of PDAM when bound to a metal, (M) .................................................127

83. Fluorescence spectrum of 2x10-5

M PDAM as a function of emission intensity

(a.u.) versus wavelength (nm). Excitation wavelength = 250 nm ..........................128

84. Fluorescence spectra of 2x10-5

M PDAM as a function of Zn(II) concentration,

in exponent-form notation.......................................................................................129


M PDAM as a function of Gd(II) concentration,



M PDAM as a function of Cd(II) concentration,



M PDAM as a function of Sc(II) concentration,



M PDAM as a function of Pb(III) concentration,



M PDAM as a function of Pb(III) concentration,

in exponent-form notation...................................................................................... 134


M PDAM as a function of Lu(III) concentration,


91. UV/Vis spectra of PDAM degradation experiment ................................................137

92. The polynomial equation of strain energy (U) for [M(PDAM)(H2O)2]3+ as a

function of M-N bond length determined by MM calculations. .............................139

93. Predicted structure of [Y(PDAM)(NO3)3] through MM calculations .....................140

xvii

INTRODUCTION

Ligands in Nuclear Waste Treatment

As the demand for energy increases at alarming rates, there has been a growing

awareness of the need to find efficient sources of energy. As of 2005, nuclear power provided

6.3% of the world’s energy and 15% of the world’s electricity [1]. Countries that use the most

nuclear energy as fuel include the United States, France, and Japan. When combined together,

they account for 56.5% of nuclear generated electricity. Many countries have considered nuclear

energy because it is a sustainable energy source with a low emission rate on greenhouse gases.

Consequently, a key problem the nuclear energy industry faces is the radioactivity of its waste

that spent nuclear fuel generates. Even with this risk posed, many countries such as Jordan,

Malaysia, Vietnam, Indonesia, United Arab Emirates and Nigeria are turning to nuclear power

plants as their major source of energy, thereby increasing the importance of reprocessing of spent

nuclear fuel.

There are many important chemical reactions that occur in a nuclear reactor. The most

common source of fuel source during the nuclear process is uranium-235, U235

. The other isotope

present in nuclear waste, U238

, undergoes transmutation when a neutron collides with U238

causing it to trans-mutate into a larger element, plutonium-239, P239

. This isotope in turn trans-

mutates into larger metal ions which are called the trans-uranium elements. Particular trans-

uranium ions of interest in the reuse of nuclear fuel are americium(III), Am(III), and curium(III),

Cm(III) as shown in Figure 1.

2

Figure 1. Trans-uranium elements formed in a nuclear reactor.

Ongoing research is being conducted to find a suitable treatment of nuclear waste to

minimize the hazards it poses. One of the solutions to this research has been the development

and utilization of the PUREX process [2]. Currently, this is the most developed and widely used

way of reprocessing nuclear waste in the industry. PUREX is an acronym standing for Plutonium

and Uranium Recovery by Extraction. This process is a liquid-liquid extraction method used to

recycle uranium and plutonium, the two main contributors of radiotoxicity of spent nuclear fuel.

By undergoing the PUREX process, this greatly reduces the radiotoxicity of nuclear waste, but

the remaining waste is still radioactive for thousands of years. The remaining contributors to the

radiotoxicity are due to the minor actinide (An) ions, which are mainly americium, Am(III), and

curium, Cm(III), including fission products. The main goal in the treatment of this waste is to

decrease its volume and radiotoxicity to suitable levels by isolating these elements and

converting them to less toxic elements. Figure 2 demonstrates the principle of the PUREX

process for the reprocessing of spent nuclear waste.

3

Figure 2. Diagram of the PUREX process for the separation of uranium and plutonium from

fission products.

4

As seen in Figure 2, the first step of the separation of nuclear waste begins with the

dissolution of irradiated fuel in aqueous nitric acid. The organic solvent extraction is composed

of 30% tributyl phosphate (TBP) in kerosene. The aqueous and organic phases are mixed

thoroughly to allow the uranium and plutonium to transfer into the organic phase. The minor

actinides and smaller metals including the fission products remain in the aqueous phase. Further

extractions allow uranium to be separated from plutonium to be recycled as fuel.

The minor actinides from the aqueous phase can also be re-used as fuel [3]. Vast research

in solvent extraction has allowed the use of ligands as extractants. Therefore, the metal is

selectively extracted from an aqueous solution of the waste into an organic phase using an

extracting ligand. Several ligands have been proposed as being selective for actinide ions over

lanthanides which include BTP [4],TPEN [5], 4,7-diphenyl-phen[6], TPTZ [7-10] (Figure 3).

5

NN

NN

NN

NN

N

BTP

N

N NN

N

N

TPEN

di-phenyl-phen

N

N

NN

N

N

TPTZ

Figure 3. Structures of BTP, TPEN, di-phenyl-phen, and TPTZ.

1,10-phenanthroline-2,9-dicarboxamide

The ligand investigated in this study is 1,10-phenanthroline-2,9-dicarboxamide (PDAM)

which is shown in Figure 4. This is one of the many derivatives of phenanthroline that are

studied by the Hancock research group. This ligand is designed to selectively bind to An(III) ions

over Ln(III) by utilizing the ligand design rules which are discussed below.

6

Figure 4. Summarization of the ideal characteristics of the PDAM complex.

Ligand Design Rules

Ligand design rules [11] were created to provide an organized means of development for

uses as given above. The attraction of Ln(III) and An(III) ions for ligands in solution is very

similar. By utilizing these design rules, it is possible to design solvent extractants based on their

chemistry to be selective for An(III) ions by creating a greater covalence in the M–L

(metal–ligand) bonding than their corresponding Ln(III) ions. These synthesized ligands also

contain properties that maintain selectivity against the Ln(III) ions present in spent nuclear

waste, as well as smaller metal ions such as Cu(II) and Zn(II). The three main areas of focus in

ligand design rules are as follows: chelate ring size theory, HSAB theory, and preorganization

theory.

7

Chelate Ring Size

Chelate ring size refers to the ring that is formed between chelating donor atoms from a

ligand to metal bond. The following graphic demonstrates the difference in chelate ring size

between the formation of five-membered and six-membered rings. The selectivity for PDAM is

excellent for large metal ions, because of the presence of the three five-membered chelate rings

[12] which lead to the selectivity for larger metal ions.

N N N N

MM

ideal M-N~ 1.5 Å

ideal M-N~ 2.5 Å

five-membered six-memberedchelate ring of phen chelate ring of DPN(1,10-phenanthroline) (dipyridonaphthalene)

This is due to the characteristic of larger metal ions experiencing more destabilization

than smaller metal ions as the chelate ring size increases. 1,10-Phenanthroline forms a 5-

membered chelate ring upon binding the metal, M, to nitrogen, N, which shows that the ideal M-

N bond length of 2.5 Å. However, DPN forms a 6-membered chelate ring and has a ideal M-N

bond length of only 1.5 Å. These bond lengths represent the most geometrically ideal angles and

lengths to minimize the structural strain. The formation of the five-membered chelate ring in this

complex is also selective for larger metal ions with an ionic radius close to 1.0 Å which includes

the An(III) and Ln(III) ions, as well as other An cations such as Th(IV) and UO22+

cation which

are present in nuclear waste.

8

HSAB Theory

The hard and soft acid base (HSAB) theory was first observed by Glenn Seaborg [13]

who discovered the M-L bonding of An cations as having greater covalence than their analogous

Ln cations. Ralph Pearson popularized the theory in which he simply states that hard acids bind

strongly to hard bases and soft acids bind strongly to soft bases. [14] This assumption was

supported by observing the log K1 values. By utilizing these rules, ligands like L1 and BTP are

used as extractants because the An(III) ions are more covalent in their metal to ligand (M-L)

bonding than the Ln(III) ions. Table 1 shows a summary of hard and soft acids and bases on a

periodic table observed by Pearson. Pearson states hard bases contain high electronegativity, low

polarizability, and are small in size. On the other hand, soft bases have low electronegativity, low

polarizability, and are relatively large in size. Hard acids include properties such as low

electronegativity, low polarizability, and are small size, while soft acids behave conversely. The

classification of Lewis acids and bases as soft, hard and intermediate are shown Figure 5.

9

1

H

3

Li

4

Be

11

Na

12

Mg

19

K

20

Ca

21

Sc

22

Ti

23

V

24

Cr

25

Mn

26

Fe

27

Co

28

Ni

29

Cu

30

Zn

31

Ga

32

Ge

33

As

37

Rb

38

Sr

39

Y

40

Zr

41

Nb

42

Mo

43

Tc

44

Ru

45

Rh

46

Pd

47

Ag

48

Cd

49

In

50

Sn

51

Sb

55

Cs

56

Ba

57

La

72

Hf

73

Ta

74

W

75

Re

76

Os

77

Ir

78

Pt

79

Au

80

Hg

81

Tl

82

Pb

83

Bi

87

Fr

88

Ra

89

Ac

Figure 5. Classification of metal according to HSAB principle and illustration of periodic table

trend.

10

Table 1. Classification of hard and soft acids and bases by HSAB principle.

_________________________Classification of Lewis Acids_______________________

___________Class (a)/Hard________________________Class (b)/Soft______________

H+, Li

+, Na

+, K

+ Cu

+, Ag

+, Au

+, Tl

+, Hg

+, Cs

+

Be2+

, Mg2+

, Ca2+

, Sr2+

, Sn2+

Pd2+

, Cd2+

, Pt2+

, Hg2+

Al3+

, Se3+

, Ga3+

, In3+

, La3+

CH3Hg+

Cr3+

,Co3+

,Fe3+

,As3+

,Ir3+

TI3+

, TI(CH3)3, RH3

Si4+

,Ti4+

,Zr4+

,Th4+

,Pu4+

,VO2+

RS+, RSe

+, RTe

+

UO22+

, (CH3)2Sn2+

I+, Br

+, HO

+, RO

+

BeMe2, BF3, BCl3, B(OR)3 I2, Br2, INC, ETC

Al(CH3)3, Ga(CH3)3, In(CH3)3 Trinitrobenzene, etc.

RPO2+, ROPO2

+ Chloranil, quinines, etc.

RSO2+, ROSO2

+, SO3 Tetracyanoethylene, etc.

I7+

, I5+

, Cl7+

O, Cl, Br, I, R3C

R3C+, RCO

+, CO2, NC

+ M

n+ (metal atom)

Bulk metals

HX(hydrogen-bonding molecule)

Borderline

Fe2+

, Co2+

, Ni2+

, Cu2+

, Zn2+

, Pb2+

B(CH3)3, SO2, NO+

__________________________Classification of Lewis Bases______________________

___Hard___________________________________Soft__________________________

H2O, OH-, F

- R2S, RSH, RS

+

CH3CO2, PO43-

, SO42-

I-, SCN

-, S2O3

2-

Cl-, CO3

2-, ClO4, NO3

- R3P, R3AS, (RO)3P

ROH, RO-, R2O CN

-, RNC,CO, RCONH2

NH3, RNH2, N2H4 C2H4, C6H6

__________________________________________H+, R

-_________________________

_________________________________Borderline______________________________ _

C6H5NH2, C5H5N, N3-, Br

-, NO

2-, SO3

2-, N2_______________

11

Donor Atoms

The atoms within ligands that serve as points of contact with a metal ion are called donor

atoms. These atoms also play a big role in the selectivity of metal ions by following the trends

according to HSAB theory. Therefore, the S-donors and N-donors from L1 and BTP respectively

lead to selectivity against the very hard Ln(III) ions according HSAB (Figure 6). Nitrogen

donors are favored widely in the use of coordination chemistry because they allow a suitable

place to bind to the metal and allow enhanced selectivity for An(III) over Ln(III) by allowing a

greater covalence between the N-donors in the M-N bond. Table 2 demonstrates the affinity of

N-donors for select metal ions. PDAM also contains an amide (carbamoyl) group that is similar

to the O-donor of tributyl phosphate, TBP, in that they are strong Lewis bases that favor large

metal ions [15] like An(III) and Ln (III). These amide groups also allow their adjacent phen-type

N-donors to be very weak proton bases. These unsaturated nitrogens are sp2

hybridized which

allow them to bind more covalently to a metal ion. Because they have low basicity, this will

allow for the formation of a strong complex which relies not only on formation constants but also

the ability of the removal of protons from donor groups in order to allow complex formation.

P

OO

OO

TBP

P

S

SH

L1

N

N

N

N

N

N

N

BTP

Figure 6. Structures for L1 and BTP and TBP.

12

Table 2. Formation constants for ammonia complexes in aqueous solution for a selection of

metal ions. [16]

Metal Ion Log K1

NH3

Ni2+

2.7

Zn2+

2.2

Sc2+

(0.7)

Cu2+

4.0

In3+

(4.0)

UO22+

(2.0)

Y3+

(0.4)

Th4+

(0.4)

Cd2+

2.6

Ca2+

-0.2

Bi3+

(5.1)

Pb2+

1.6

Am3+

(2.7)

La3+

(0.2)

Gd3+

(0.5)

Lu3+

(0.7)

The idea behind PDAM is that the electron-withdrawing nature of the amide groups will

lower the affinity for Cu(II) and other small ions for the ligand by reducing the donor strength of

the N-donors on PDAM. If PDAM possesses these qualities it will prove to be an excellent

candidate for the extraction of the minor actinides Am(III) and Cm(III) from nuclear waste to be

re-used as an energy source.

13

Preorganization

There has been considerable research in Dr. Hancock’s group on the selective extractants

for Am(III) and Cm(III) with the discovery of a new class of ligands such as PDA [17], DPP

[18], and PDALC [19] as seen in Figure 7 below:

Figure 7. The Structures of PDA, PDAM, DPP, 1,10-phen and PDALC.

These ligands which are analogs of PDAM are all highly preorganized because of the presence

of the rigid 1,10-phenanthroline backbone which holds the donor atoms in the position required

for complexing with the larger metal ions. Figure 8 demonstrates the meaning of preorganization

with PDAM and Bis-2,2’:6’,2”:6”,2’’’-quaterpyridine(QUATERPY).

N NO

-O

OO-

PDA

N NO

H2N

ONH2

PDAM

N N

N NDPP

N N

1,10-phen

N N

HOOH

PDALC

14

a)

N

N

N

N

b)

N N

O

H2N

O

NH2

Figure 8. a) Chemical structure of QUATERPY compared to b) chemical structure of PDAM to

illustrate preorganization.

Figure 8 illustrates how QUATERPY can freely rotate. By doing so creates a larger

amount of energy for the ligand to overcome in order for it to bind to a metal ion. This results in

a smaller stability constant, log K1. With the addition of the ethylene bridge, this forms a

phenanthroline backbone which is fixed into position making it unable to rotate around the bond.

By having the nitrogen donor groups on the 2 and 9 positions of the phen backbone, this allows

the ligand to have a higher degree of preorganization. [20]

15

METHODS AND MATERIALS

General

All chemicals and reagents used were of analytical grade and purchased commercially.

Aqueous metal-ligand solutions were made using deionized water (Milli-Q, Waters Corp.) of

>18 MΩ.cm-1

resistivity.

To determine the purity of the PDAM ligand and its intermediates FT-IR analysis,

melting point analysis, and 1H-NMR were analyzed. The final products and intermediates of the

synthesis were prepared for 1H-NMR analysis in DMSO-d5.

1H-NMR spectra were performed

using a Bruker 400 MHz NMR spectrometer. The synthesis products were prepared for FT-IR

analysis as KBr pellets (Alfa Aesar, 99%) and spectra were taken using a Thermo Scientific

Nicolet 6700 FT-IR spectrometer with OMNIC32 Version 2.09 software. The melting point

analysis was also performed using a Haake Buchler melting point apparatus.

Synthesis of PDAM

The synthesis of PDAM was carried out as described in the literature [21,22] with a few

modifications. Characterization of the products was performed using FT-IR analysis, NMR, and

melting point analysis.

Synthesis of 1,10-phenanthroline-2,9-dicarboxaldehyde (PDALD)

A mixture of 3.0058 g 2,9-methyl-1,10-phenanthroline hemihydrate (13.84 mmol, Alfa

Aesar, 98+%) and 7.5002 g selenium dioxide (67.59 mmol, Alfa Aesar, 99.4%) was placed in a

250 ml round-bottom flask. The compounds were dissolved in 200 ml of 95% p-dioxane (Alfa

Aesar, 99+%)/5% milliQ water. The mixture was then heated to 122 oC in a wax bath while

16

stirring, and was allowed to reflux for 3 hours. The hot solution was filtered through celite by

vacuum filtration and placed in a freezer overnight. The solution thawed to room temperature

and the precipitate that was formed was collected on a glass-frit through filtration. The product

was allowed to dry then weighted yielding 1.9904g of un-pure product, the percent yield was

(8.43 mmol, 60.88%)

Synthesis of 1,10-phenanthroline-2,9-dicarboxylic acid (PDA)

A solution 1.9904 g of non-purified 1,10-phenanthroline-2,9-dicarboxaldehyde (8.42

mmol) was placed into a 250mL round bottom flask and dissolved in 80 mL of a 4:1 HNO3 (15.8

N, Fisher Scientific)/H2O mixture and stirred and refluxed at 122oC for 10 hours. After 10 hours,

the solution was taken off the heat and allowed to cool to room temperature then placed into a

freezer for 48 hours. During this time yellow crystals formed at the bottom of the flask. These

crystals were gravity filtered through filter paper then allowed to dry. The dry crystals were

weighted to give a yield of 0.9866g (3.68 mmol, 43.71%).

Synthesis of 2,9-Bis(carbomethoxy)-1,10-phenathroline (PBE)

0.9866 g (3.68 mmol) of 1,10-phenanthroline-2,9-dicarboxylic acid was placed into a

250mL round bottom flask along with 125mL of anhydrous methanol. 5mL of concentrated

H2SO4 was added to the solution to catalyze the esterification of the carboxylic acid. The

solution was heated to reflux for 4 hours; the solution was then allowed to cool to room

temperature. Once the solution was at room temperature the acid was neutralized using saturated

Na2CO3. The desired product fell out of solution once when the pH was neutral. The product was

gravity filtered and allowed to dry, giving an overall yield of 0.5863g (1.98 mmol, 53.80%).

17

Synthesis of 1,10-phenanthroline-2,9-diamide (PDAM)

0.5863g (1.98 mmol) of PBE was placed into a 250mL round bottom flask along with

200mL of 28% ammonia (28% w/w aq. soln., Alfa Aesar) and 0.6 g ammonium chloride (99%,

VWR). The mixture was then stoppered and vented by using a syringe needle and stirred for 24

hours; after that period the solution was then gravity filtered and allowed to dry yielding 0.1811

g (0.68 mmol, 34.34%) of product.

18

NN

H3C CH3

neocuproine

NN

O=C C=O

PDALD

1.)SeO2

2.)p-dioxane/5% H2O

H H

4:1 HNO3:H2O

NN

HOOC COOH

PDA

NN

H3COC COCH3

O O

H2SO4/MeOH

PBE

NN

H2NC CNH2

O O

NH3

PDAM

Figure 9. Schematic of the synthesis of PDAM.

19

UV/Vis Spectroscopy

Metal Solutions

UV/Vis spectrophotometry was used to monitor complexation of aqueous PDAM

solutions by addition of various aqueous metal solutions. Because the solubility of PDAM in

water is low, a stock solution of 1.00x10-3

M PDAM (0.0266g in 100mL of methanol) was made

up fresh and used in each of the titration experiments. A 50.0 mL solution of 2.00x10-5

M PDAM

was prepared by the addition of 1000±0.05µL of 1.00x10-3

M PDAM. The ionic strength for the

solution was held constant with 0.1M NaClO4 (0.6123g into 50mL H2O, Alfa Aesar, 98%). To

control dilution, 1000±0.05µL of 1.00x10-3

M PDAM was added to the metal solution. Stock

solutions of each metal used in the UV/Vis experiments were made in 50 mL volumetric flasks

and filled to the appropriate volume. Table 3 summarizes the procedure for each metal stock

solution. The 50.00±0.05 mL PDAM solution was placed into the flow cell apparatus. The pH of

the solution was monitored, and the meter was calibrated using a 4, 7, 10 buffer system.

In the event that small amount of metal solution formed the complex with PDAM,

another experiment was conducted by using acid-base titration in the presence of a competing

ligand. A 1:1:1 ratio of 2.00x10-5

M solution of PDAM, competing ligand, and metal were

prepared in the same manner as described above. This solution was acidified with 11.6 M HClO4

to an initial pH of 2. The ionic strength for the solution was held constant with 0.09 M NaClO4

(0.6123g into 50mL H2O, Alfa Aesar, 98%). The solution was titrated with 0.1 M NaOH to a

final pH of around 7. Table 3 summarizes the procedure for each competition reaction.

20

Table 3. Summary of prepared metal solutions.

Metal Analyzed Company

Formula

Weight (g/mol) Mass (g)

[Metal

Ion] [PDAM]

Zn(ClO4)2*6H2O Alfa Aesar 372.36 6.2057 0.3333 2*10-5

Cd(ClO4)2*6H2O Alfa Aesar 419.40 0.0677 0.003230 2*10-5

Ni(ClO4)2*6H2O Alfa Aesar 365.68 1.8284 0.1000 2*10-5

Ca(ClO4)2*6H2O Strem Chem. 311.40 11.949 1.0006 2*10-5

Cu(ClO4)2*6H2O Alfa Aesar 372.54 0.0656 0.003522 2*10-5

Sc(ClO4)3*6H2O Alfa Aesar 451.40 0.1517 (50% w/w) 0.003361 2*10-5

Y(NO3)3*6H2O Aldrich 383.01 0.0638 0.003332 2*10-5

UO2(NO3)2*6H2O Fisher 502.13 0.0888 0.003535 2*10-5

Th(NO3)4*4H2O J. T. Baker 552.15 0.0920 0.003488 2*10-5

La(ClO4)3*6H2O Aldrich 437.26 0.0730 0.003339 2*10-5

Ce(ClO4)3 Aldrich 438.47 0.1941 (40% w/w) 0.003541 2*10-5

Pr(ClO4)3 Aldrich 439.26 0.1868 (40% w/w) 0.003402 2*10-5

Nd(ClO4)3*6H2O Alfa Aesar 550.69 0.1864 (50% w/w) 0.003385 2*10-5

Sm(ClO4)3 Aldrich 448.70 0.1929 (40% w/w) 0.003439 2*10-5

Eu(OSO2CF3)3*2H2O Alfa Aesar 635.20 0.1067 0.003360 2*10-5

Gd(ClO4)3*6H2O Alfa Aesar 563.70 0.1879 (50% w/w) 0.003333 2*10-5

Tb(ClO4)3*6H2O Alfa Aesar 565.37 0.2011 (50% w/w) 0.003557 2*10-5

Dy(ClO4)3 Aldrich 460.85 0.2276 (40% w/w) 0.003951 2*10-5

Ho(ClO4)3 Aldrich 463.28 0.1894 (40% w/w) 0.003271 2*10-5

Er(ClO4)3 Aldrich 465.61 0.1952 (40% w/w) 0.003354 2*10-5

Tm(CF3SO3)3 Aldrich 616.14 0.1030 0.003343 2*10-5

Yb(NO3)3*5H2O Aldrich 449.13 0.0748 0.003400 2*10-5

Lu(ClO4)3*6H2O Alfa Aesar 581.41 0.1938 (50% w/w) 0.003998 2*10-5

21

Table 4. Summary of prepared competition reaction solutions. Note: competing ligand, metal

ion, and PDAM all diluted from 1.0*10-3

stock solutions.

Metal Analyzed Company

Formula

Weight

(g/mol)

Competing

Ligand

[Competing

Ligand]

[Metal

Ion] [PDAM]

Cd(ClO4)2*6H2O

Alfa

Aesar 419.40 EDTA 2*10-5

2*10-5

2*10-5

Cd(ClO4)2*6H2O

Alfa

Aesar 419.40 TETREN 2*10-5

2*10-5

2*10-5

Pb(ClO4)2*3H2O

Alfa

Aesar 460.15 TETREN 2*10-5

2*10-5

2*10-5

Bi(NO3)3*5H2O Aldrich 485.07 TETREN 2*10-5

2*10-5

2*10-5

In(ClO4)3*8H2O Aldrich 557.26 TETREN 2*10-5

2*10-5

2*10-5

22

Flow Cell Set-Up

PDAM has intense bands in the 200-350 nm region of the spectrum which allowed the

use of a UV spectroscopic study to find its protonation constants and metal ion complexation

equilibria in 0.1 M NaClO4 possible as reported by previous work on other phen-based ligands.

[11,17-19,23] UV/Vis absorbance spectra were recorded for aqueous metal-ligand titration

experiments using a double beam Cary Bio 1E UV/Vis spectrophotometer (Varian, Inc.) with

WinUV Version 2.00(25) software. A 1.0cm quartz flow cell (VWR) was connected by tubing to

an external titration cell with a variable flow peristaltic pump to allow a continuous circulation of

the metal-ligand solution while each titrant addition was made to the external cell. The solutions

were maintained at a constant 25.0+0.1 oC throughout the experiment. Figure 10 shows a

diagram of the flow cell apparatus. Between each titrant addition the solution was allowed to

equilibrate for 7 minutes to ensure titrant equilibration. The absorbance spectra were referenced

using deionized H2O and a 1.0 cm quartz cell (VWR) filled with deionized H2O was placed in

the path of the reference beam. The absorbance scan range was from 190 to 350 nm at a rate of

600.0 nm/min for all samples.

All pH values for the titration experiments were recorded in the using a SympHonyTM

SR60IC pH meter from VWR Scientific, Inc with a VWR SympHonyTM

gel epoxy semi-micro

combination pH electrode. The pH meter and electrode was calibrated by titrating 0.010 M

HClO4 in 0.090 M NaClO4 with 0.010 M NaOH in 0.090 M NaClO4 from which a E0

to

determine the correlation between mV readings and calculated pH. The pH meter was also

calibrated by using pH 4.00, 7.00 and 10.00 buffer solutions prior to each titration. Aqueous

metal-ligand solutions contained a 0.10 M ClO4- as a background electrolyte.

23

Figure 10. Diagram of a flow cell apparatus used in the titration experiments.

24

Fluorescence

By using fluorescence a series of emission and excitation wavelengths can be obtained in

a three dimensional matrix of fluorescence intensity as a function of both emission wavelengths

and excitation wavelengths. The emission spectra were recorded using a Horiba Jobin Yvon

Fluororlog-3 scanning fluorometer equipped with a 450 W Xe short arc lamp and a R928P

detector. The signal to ratio mode was collected with a dark offset and using 5nm band-passes on

both the excitation and emission monochromators. Measurements were taken in 5 nm intervals

from 335 to 480 nm at 280 nm excitation wavelength. These scans were corrected for instrument

configuration using the factory supplied correction factors. The FluorEssence program [24] was

used to mask the Rayleigh and Raman scattering peaks by removing portions (± 10-15 nm FW)

of each scan centered on the respective scatter peak. The rest of the data was normalized to a

daily-determined water Raman intensity (275ex/ 303em, 5 nm band-passes). The replicate scans

were generally within 5% agreement in terms of intensity and within band-pass resolution in

terms of peak location.

A 1.0cm quartz flow cell (VWR) was connected by TygonTM

tubing to an external

titration cell with a variable flow peristaltic pump to allow a continuous circulation of the metal-

ligand solution while each titrant addition was made to the external cell. A continuous stream of

nitrogen gas was placed into the external cell to ensure proper conditions for fluorescence as

seen in Figure 11 below.

A 50.0 mL solution of 2.00x10-5

M PDAM was prepared by the addition of

1000±0.05µL of 1.00x10-3

M PDAM. The ionic strength for the solution was held constant with

0.1 M NaClO4 (0.6123g into 50mL H2O, Alfa Aesar, 98%). Stock solutions of each metal used

25

in the fluorescence experiments were made in 50 mL volumetric flasks and filled to the

appropriate volume. Table 5 summarizes the procedure for each metal stock solution.

Table 5. Summary of the preparation of fluorescence solutions.

Metal Analyzed Company FW Mass (g)

[Metal

Ion] [PDAM]

Zn(ClO4)2*6H2O Alfa

Aesar 372.36 6.2064 0.3334 2*10

-5

La(ClO4)3*6H2O Aldrich 437.26 0.0726 0.00332 2*10-5

Gd(ClO4)3*6H2O Alfa

Aesar 563.7 0.1883(50% w/w) 0.00334 2*10

-5

Lu(ClO4)3*6H2O Alfa

Aesar 581.41 0.1950 (50% w/w) 0.004 2*10-5

Cd(ClO4)2*6H2O Alfa

Aesar 419.4 0.0698 0.00333 2*10

-5

Sc(ClO4)3*6H2O Alfa

Aesar 451.4 0.1523 (50% w/w) 0.00337 2*10

-5

Pb(ClO4)2*3H2O Alfa

Aesar 460.15 0.0778 0.00338 2*10

-5

26

Figure 11. Diagram of a flow cell apparatus used in fluorescence experiments.

27

PDAM Degradation Experiment

A degradation experiment was needed to see the stability of PDAM under acidic

conditions similar to nuclear waste. A 50.0 mL solution of 2.00x10-5

M with 1.0 M HClO4 was

analyzed by UV/Vis in intervals of 3 hours over a 12 hour period. The solution was placed in a

cabinet and left for 3 months. After 3 months the solution was analyzed each consecutive month

for a total of 7 months.

Molecular Mechanics Calculations

The Hyperchem 7.5 MM+ molecular mechanics module [25] was used in order to

examine the ideal bond lengths that would best-fit sizes for metal ions with PDAM. By looking

at bond lengths such as M–N and M–O lengths we can theoretically determine the best-fit metal

ions that would bind with PDAM which will aid in metal selection.

Figure 12. The M–N and M–O bond lengths (highlighted in orange) calculated through

molecular mechanics calculations.

28

RESULTS AND DISCUSSION

Synthesis of PDAM

The synthesis of 1,10-phenanthroline-2,9-dicarboxaldehyde (PDALD) has resulted in an

impure mixture from the results of the NMR. The synthesis yielded 1.9904 g of PDALD for a

percent yield of 60.88%. The melting point for PDALD was 238° which compared to the

literature value [22] of 231-232° one would suspect that the product is partially impure. The IR

spectrum in Figure 13 shows a major product of PDALD with a peak at 1726 cm-1

for the C=O

stretch. The product which contains an aldehyde group contains a C-OH stretch at 3012 cm-1

.

This C-OH stretch shows that the aldehyde is indeed present; however it is partially oxidized into

PDA. The NMR spectrum in Figure 14 of PDALD confirms a compound containing an aldehyde

group by showing a wide peak at 10.3 ppm. The NMR spectrum also shows the aromatic region

from 8 ppm to 9 ppm. There is also a sharp peak due to an impurity at 3.6 ppm and a wide peak

at 3.5 ppm due to the presence of water. Although impure, this proves not to be a problem

because the next step in the synthesis the aldehyde is further oxidized to form PDA. Therefore,

further purification was not needed because an oxidation step was performed to produce PDA.

29

Figure 13. IR-spectra of PDALD in KBr pellet.

30

Figure 14. NMR-spectra of PDALD in DMSO-d5.

31

The PDALD product was used to synthesize 1, 10-phenanthroline-2, 9-dicarboxylic acid

(PDA). The reaction yielded .9866 g of PDA for a percent yield of 43.71%. The melting point

for the crystalline product was 243.8° which compared to the literature [22] value of 238° agrees

with the literature value. An IR analysis was also conducted and the spectrum is shown in Figure

15. The spectrum shows a clean carboxylic acid peak at 1735 cm-1

for the C=O stretch band a

peak at 1384 cm-1

for the C-O stretch. The NMR results shown in Figure 16 shows a pure PDA

product. There are 3 peaks from 8.0 to 8.7 ppm which indicate the aromatic region. The

carboxylic acid is confirmed by the IR results which indicate the carboxylic acid group by the

large bands in the C=O stretch region. The results from the melting point determination, NMR,

and IR spectrum showed a clean product of PDA from the synthesis using PDALD.

32

Figure 15. IR spectra of PDA in KBr pellet.

33

Figure 16. NMR spectra of PDA in DMSO-d5.

34

The PDA product was used to synthesize 2,9-Bis(carbomethoxy)-1,10-phenathroline

(PBE). The reaction yielded 0.9866 g of PBE for a percent yield of 53.80%. The melting point

for the crystalline product was 262.4° which compared to the literature [22] value of 213-214°

which also does not agree well with the literature value. There are no other literature values

listed for PBE so further analysis must be done in order to determine the purity of the PBE

product. An IR analysis was also conducted and the spectrum is shown in Figure 17. The

spectrum shows a strong C=O stretch band at 1735 cm-1

which is characteristic for an ester-

containing compound. The NMR spectrum is shown in Figure 18. The results showed

confirmation of PBE with a sharp peak at 4.0 ppm which represents the methyl groups on the

ester. These results from the melting point determination, NMR, and IR spectra showed a clean

product of PBE from the synthesis using PDA.

35

Figure 17. IR-spectra of PBE in KBr pellet.

36

Figure 18. NMR-spectra of PBE in DMSO-d5.

37

The PBE product was used to synthesize 2,9-diamide-1,10-phenathroline (PDAM). The

reaction yielded 0.1811 g of PDAM for a percent yield of 34.34% with an overall yield of

4.92%. The melting point for the crystalline product was 361°C which compared to the literature

value of >300°C agrees with the literature [22] value. However, other results needed to be

examined in order to determine the purity of the product because the melting point information

that was provided was not as accurate. An IR analysis was also conducted and the spectrum is

shown in Figure 19. The spectrum shows a strong N-H stretch in the region between 3100-3400

cm-1

which is characteristic of amides. There is also a strong C=O stretch band at 1692 cm-1

which is attributed to the carbonyl groups on the compound. The NMR spectrum was also

performed and is shown in Figure 20. The presence of an amide groups was indicated with two

peaks representing the hydrogens on the amide groups at 7.9 and 8.9 ppm. Although the melting

point determination could not fully determine the purity of PDAM, NMR and IR spectra

performed showed a clean product of PDAM from the synthesis using PBE.

38

Figure 19. IR-spectra of PDAM in KBr pellet.

39

Figure 20. NMR-spectra of PDAM in DMSO-d5.

40

UV/Vis Titrations of PDAM

The titration experiments were performed utilizing UV/Vis spectroscopy as an analytical

tool to detect metal complex formation involving PDAM. By obtaining the protonation constant

(pK) of the ligand, it is then possible to determine the strength of which different metal ions can

bind to PDAM. Because the solubility of PDAM is quite low, a concentration of 2x10-5

M of free

PDAM in 1.0 M HClO4 at 25.0+/-0.1°C in 1.0 M NaClO4 for ionic strength was prepared as

described above. The initial pH was calculated until a pH of 2.38 was recorded because the pH

probe could be ruined if under very acidic conditions for prolonged periods of time. The

solution was titrated with a 1.0 M solution of NaOH with the final pH being 10.89. After each

addition of NaOH, the absorbance spectra were taken from 190 nm to 350 nm. The free ligand

titration set of spectra as a function of pH are shown in Figure 21. Absorbances were recorded at

231, 264, 284, and 294 nm because these wavelengths showed the greatest change in absorbance.

A pK of 0.6 ± 0.1 could be fitted by varying absorbance as a function of pH at these 4 selected

wavelengths. This is the lowest protonation constant that has been reported [26] for a phen

derivative. The protonation constant for phen is 5.2, [26] and for 5-nitro-phen, the lowest

observed before PDAM, was 3.22. The reason for PDAM possessing such a low protonation

constant could be from the presence of amide groups which are strongly electron withdrawing, as

seen with picolinamide [26] with a pK of 1.8. These data points were used to create plots of

absorbance versus pH. This experiment shows the dissociation of a proton from the ligand as

shown in Equation 1.

𝐿𝐻+ ↔ 𝐿 + 𝐻+ (1)

41

Figure 21. UV-Vis absorbance spectrum of the titration of PDAM at 2.00x10-5

M

42

Figure 22. Protonation equilibrium for 2,9-diamide-1,10-phenanthroline (PDAM).

43

Log K1 Results for Metal Ions with PDAM

The metal ions that were complexed with PDAM were chosen based on varying ionic

radii and ionic charge. Because PDAM has a low protonation constant 0.6 meant that the

competition between the metal ion and the proton for coordination to the ligand could not be

used for the determination of log K1. Instead, a 50.0 mL stock solution of 2.00x10-5

M PDAM

was prepared and placed into the sample container in which multiple additions of the aqueous

metal in interest were added to the PDAM solution and absorbance values were recorded. By

measuring the variation of the absorbance 2.00x10-5

M PDAM solutions as a function of metal

ion concentration in titrations with 0.1 M NaClO4 was found to be an acceptable method of

analyzing the complexation of the metal and PDAM. Table 6 summarizes the log K1 for select

metal-1,10-phenanthroline and metal-PDAM complexes.

44

Table 6. List of log K1 for PDAM to log K1 of 1,10-phen complexes [26] with various metal ions

in order of ionic radii (Å)

Metal

Ion

Ionic

Radii

(Å)

Log K1

PDAM

Log K1

1,10 -

phen

ΔLog

K1

Ni2+

0.69 3.06 8.70 -5.64

Zn2+

0.74 3.77 6.38 -2.61

Sc3+

0.75 4.55 ---- ----

In3+

0.80 9.43 5.70 3.73

UO22+

0.86 4.33 ---- ----

Cu2+

0.87 3.56 ---- ----

Y3+

0.93 3.45 ---- ----

Th4+

0.94 5.01 5.73 -0.72

Cd2+

0.95 7.05 5.66 1.39

Ca2+

1.00 1.94 1.00 0.94

Bi3+

1.03 9.44 ---- ----

Pb2+

1.19 5.82 4.62 1.20

During the titration analysis, the metal ion binds to the ligand and the peak shifts are observed

when looking at the UV/Vis spectra of the free ligand. This is shown in Equation 2 below:

𝑀𝑋+ + 𝐿 → 𝑀𝐿𝑋+ (2)

Shown above is the example of the addition of metal to the ligand which produces a complex.

The log K1 for the complex (ML) is calculated by the following steps. The evidence of the

formation of the complex is shown by an inflection of absorbance versus the log of the

concentration of metal. Absorbance values were modeled as a function of the log of the

concentration for each titration experiment. The concentration of each addition was calculated by

using Equation 3 below:

𝑅𝑒𝑎𝑙 𝑀𝑒𝑡𝑎𝑙 =𝑇𝑜𝑡𝑎𝑙 𝑀𝑒𝑡𝑎𝑙 𝑉𝑜𝑙 ∗[𝑀𝑒𝑡𝑎𝑙 ]

𝑉𝑜𝑙𝑢𝑚𝑒 𝑖𝑛 𝐶𝑒𝑙𝑙 (3)

45

The real concentration of the metal is observed for each addition. This represents total metal

volume represents the volume added to the solution which is multiplied by the concentration of

the metal. The product of the total metal volume and concentration of the metal is divided by

volume of the cell which is the original 50.0 mL PDAM solution plus the total metal volume.

The log of this value is used to plot absorbance as a function of the log of the concentration of

the metal. Because the ligand was added to the metal solution there is no need to correct for

dilution. The theoretical values for absorbance were calculated by using the formula 3, 4, and 5

below,

𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 1: 10 𝑀𝑒𝑡𝑎𝑙 × 𝑅𝑒𝑎𝑙 (4)

𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 2: 1 + 𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 1 (5)

𝐴𝑏𝑠.𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 = 1

𝐸𝑞 .1× 𝑎𝑏𝑠. 𝐿 + (

𝐸𝑞 .1

𝐸𝑞 .2× 𝑎𝑏𝑠 𝑀𝐿) (6)

Equation 4 represents the species of ligand whereas Equation 5 represents the species of the

metal-ligand complex. These values are used in Equation 6 above to calculate the theoretical

absorbance. The difference of the two absorbances is represented in Equation 7 below:

𝑑𝑖𝑓𝑓 = 𝑎𝑏𝑠 𝑡ℎ𝑒𝑜𝑟 − 𝑎𝑏𝑠 𝑜𝑏𝑠 (7)

The standard deviations of these differences were used in the SOLVER module so that they were

minimized. The points in the plots are the observed values of absorbance. The theoretical curves

of absorbance versus log of the concentration were fitted to the experimental points using the

SOLVER module of the program EXCEL. Results for individual metal ions are discussed below.

46

Nickel(II)-PDAM results

Nickel has an ionic radius of 0.69 Å and is an intermediate acid according to the HSAB

principle. Nickel is the smallest metal analyzed and was expected to bind weakly with PDAM

compared to the other larger metals analyzed. Due to the chelate ring size rules discussed

previously, nickel forms a 5-membered ring when binding to PDAM which is unfavorable for

small metal ions.[12] A solution of 0.10M Ni(ClO4)2 was added to 2x10-5

M PDAM with 0.1M

NaClO4 at a pH held at 5.37. The UV/Vis spectra plotting absorbance versus log of the

concentration of Ni(ClO4)2 are show in Figure 23. Absorbances were recorded at 316, 283, 248,

235, 217, 209 nm because these wavelengths exhibited the largest change in absorbances. The

theoretical and measured absorbances were plotted for every wavelength by minimizing the sum

of the squares as shown in Figure 24. Table 7 summarizes the solutions of each parameter that

was changed by SOLVER. This program was used to minimize the standard deviation so that a

more accurate log K1 value could be calculated. The log K1 was calculated to be 3.06 by using

Equations 2-7 mentioned above.

47

Figure 23. UV/Vis spectra of PDAM (2x10-5

M) and Ni(ClO4)2 (0.10 M) with 0.1 M NaClO4

present held at a pH 5.37.

48

Figure 24. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Ni] for

titration of PDAM and Ni(ClO4)2. The midpoints in the inflections of the curves indicate the log

K1 value for PDAM .

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-7.00 -6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00

Ab

sorb

ance

log[Ni]

316 nm

316 nm Theoretical

283 nm

283 nm Theoretical

248 nm

248 nm Theoretical

235 nm

235 nm Theoretical

217 nm

217 nm Theoretical

209 nm

209 nm Theoretical

49

Table 7. Solutions and standard deviation for each parameter used by SOLVER module of

EXCEL in the determination of log K1 of PDAM-Ni complex.

Overall Parameter Solution

Standard

Deviation

log K1 3.06 0.005359

316 nm abs L 0.147

0.001640 abs ML 0.124

283 nm abs L 0.468

0.007170 abs ML 0.501

248 nm abs L 0.487

0.005598 abs ML 0.398

235nm abs L 0.702

0.003315 abs ML 0.617

217nm abs L 0.435

0.003315 abs ML 0.497

209 nm abs L 0.463

0.048987 abs ML 0.568

50

Zinc(II)-PDAM results

Zinc has an ionic radius of 0.74 Å which is slightly smaller than the ideal 1.0Å ionic

radius for PDAM. Zinc is classified as an intermediate acid according to the HSAB. The log K1

for [Zn(PDAM)]2+

complex is supposed to be higher than the [Ni(PDAM)]2+

due to the larger

ionic radius of zinc. The UV/Vis absorbance spectra for Zn(II) additions with PDAM are shown

in Figures 25 and 26. A plot of the corrected absorbance values versus log of the concentration of

Zinc(II) is shown in Figure 27. From the selected wavelengths of 315, 289, 282, 248, 235, 217,

204 nm a log K1 of 3.77 was calculated using Equations 2-7 from the data using the process as

described above. Table 8 summarizes the solutions of each parameter that was changed by

SOLVER.

The spectra did not show any isosbestic points, however there is a slight shift in

wavelength which indicates the complex did form. Another analysis as shown in Figure 26, was

performed under the same concentrations, however, the solutions for PDAM and the aqueous

metal were acidified to a pH of 4 to ensure that the amides on the ligand were not hydrolyzed.

There were no changes between the two spectra shows that there was no hydrolysis on the

amides of the ligand.

51


M) and Zn (0.3333 M) with 0.1 M NaClO4 present.

Initial pH at 5.31.

52


M) and Zn (0.3333 M) with 0.1 M NaClO4 present.

Initial at pH 4.19.

53

Figure 27. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Zn] for

titration of PDAM and Zn(ClO4)2.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -7.00 -6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00

Ab

sorb

ance

log[Zn]

315 nm

315 nm Theoretical

289 nm

289 nm Theoretical

282 nm

282 nm Theoretical

248 nm

248 nm Theoretical

235 nm

235 nm Theoretical

217 nm

217 nm Theoretical

204 nm

204 nm Theoretical

54


EXCEL in the determination of log K1 of PDAM-Zn complex.


Standard

Deviation

log K1 3.77 0.005618

315 nm abs L 0.160

0.000509 abs ML 0.152

289 nm abs L 0.425

0.007750 abs ML 0.563

282 nm abs L 0.493

0.000954 abs ML 0.486

248 nm abs L 0.532

0.001253 abs ML 0.501

235nm abs L 0.731

0.011448 abs ML 0.597

217nm abs L 0.467

0.006949 abs ML 0.542

204 nm abs L 0.492

0.010460 abs ML 0.587

55

Scandium(III) Results

Scandium has an ionic radius of 0.75Å and is classified as a hard acid, which is closer to

the ideal 1.0 Å ionic radius for the complexation of the nitrogen and oxygen donor atoms of

PDAM. A solution of 3.36 x 10-3

M Sc(ClO4)3 was added to 2x10-5

M PDAM with 0.1M

NaClO4. The UV/Vis spectra plotting absorbance versus log of the concentration of Sc(ClO4)3

are shown in Figure 28. The spectra of the complexation of PDAM with Sc(III) shows evidence

of the formation of the complex by the multiple isosbestic points located throughout the spectra.

Absorbances were recorded at 297, 284, 256, and 235 nm because these wavelengths exhibited

the largest change in absorbances. The theoretical and measured absorbances were plotted for

every wavelength by minimizing the sum of the squares as shown in Figure 29. SOLVER was

used to minimize the standard deviation so that a more accurate log K1 value can be calculated.

Table 9 outlines the solutions of each parameter that was varied using SOLVER along with the

standard deviation of each variable. The log K1 was calculated to be 4.55 by using Equations 2-7

mentioned above. The increase in ionic radii allows the complexation Sc(III) to become easier

and require less energy as compared to the Ni(II) and Zn(II) as shown by the smaller values in

log K1.

56


M) and Sc(0.003361 M) with 0.1 M NaClO4

present. Initial pH at 2.14.

57

Figure 29. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Sc] for

titration of PDAM and Sc(ClO4)3.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -7.00 -6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00

Ab

sorb

ance

log[Sc]

297 nm

297 nm Theoretical

284 nm

284 nm Theoretical

256 nm

256 nm Theoretical

235 nm

235 nm Theoretical

58


EXCEL in the determination of log K1 of PDAM-Sc complex.


Standard

Deviation

log K1 4.55 0.003512

297 nm abs L 0.339

0.002325 abs ML 0.688

284 nm abs L 0.497

0.002743 abs ML 0.105

256 nm abs L 0.522

0.004217 abs ML 0.467

235 nm abs L 0.748

0.004886 abs ML 0.320

59

Copper (II) Results

Copper (II) has an ionic radius of 0.77 Å and is an intermediate acid according to the

HSAB principle. A solution of 0.003522M Cu(ClO4)2 was added to 2 x 10-5

M PDAM with 0.1

M NaClO4. The UV/Vis spectra plotting absorbance versus log of the concentration of Cu(ClO4)2

are show in Figure 30. Absorbances were recorded at 297, 292, 286, and 284 nm. This

experiment produced a precipitate that obscured all wavelengths below 250 nm. Therefore, the

predicted value for the log K1 of copper could be slightly inaccurate because there were several

wavelengths that could have been used in the calculation for the determination log K1, but had to

be omitted due to the charge transfer band. The theoretical and measured absorbances were

plotted for every wavelength by minimizing the sum of the squares as shown in Figure 31.

SOLVER was used to minimize the standard deviation so that a more accurate log K1 value can

be calculated. Table 10 summarizes the solutions of each parameter that was changed by

SOLVER. The log K1 was calculated to be 3.56 by using Equations 2-7 in the process mentioned

above.

60


M) and Cu(0.003522 M) with 0.1 M NaClO4


61

Figure 31. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Cu] for

titration of PDAM and Cu(ClO4)2.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

-8.00 -7.00 -6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00

Ab

sorb

ance

log [Cu]

297 nm

297 nm Theoretical

292 nm

292 nm Theoretical

286 nm

286 nm Theoretical

284 nm

284 nm Theoretical

62


EXCEL in the determination of log K1 of PDAM-Cu complex.


Standard

Deviation

log K1 3.56 0.004791

315 nm abs L 0.289

0.002647 abs ML 0.335

289 nm abs L 0.384

0.008246 abs ML 0.500

282 nm abs L 0.477

0.003739 abs ML 0.578

248 nm abs L 0.482

0.004533 abs ML 0.559

63

Indium (III) Results

Indium has an ionic radius of 0.80Å and is classified as an intermediate acid according to

the HSAB rules. This is an ideal metal ion because it binds preferably with nitrogen donors as

shown with the log K1 NH3 = 4.0. Another reason for the dramatic increase in log K1 value of

indium is shown by the sharp band that is formed at 250 nm. This sharp band is due to the π-π*

transition which in the free ligand is coupled to vibrations of the ligand that broaden the band.

When indium coordinates to PDAM to form a complex, the rigidity of PDAM in its complex

with indium increases greatly and these vibrations are no longer coupled to the electronic

transition which sharpens the appearance of that band. The presence of five-membered chelate

rings when forming a complex allows PDAM to be more selective to metal-ligand bond lengths

closer to 1.0Å which includes In(III). Indium binds so well with PDAM that metal addition

would not be able to accurately determine the log K1 value of indium with PDAM. Therefore, a

competition reaction with TETREN was used to determine a more accurate value of log K1. This

experiment was conducted by using 50.0 mL solution of 1:1:1 PDAM: In(ClO4)3:TETREN at

2.00x10-5

M and was acidified to an initial pH of 2.07. This was titrated with 0.10 M NaOH

solution to a final pH of 7.31. The UV/Vis spectra plotting absorbance versus wavelength is

shown in Figure 32. Absorbances were recorded at 294, 284, 253, and 237 nm because these

wavelengths exhibited the largest change in absorbances. A log K1 of 9.43 was calculated from

the absorbance data using the process as described above. Theoretical and measured absorbances

were plotted shown in Figure 33 for each wavelength by minimizing the sum of the squares

using SOLVER. Table 11 summarizes the solutions of each parameter that was changed by

SOLVER. The program was also used to minimize all standard deviations in order to determine

the best possible log K1 value.

64

Figure 32. UV/Vis spectra of PDAM:TETREN:In (2x10-5

M) with 0.1 M NaClO4 present. Initial

pH at 2.07 to a final pH of 7.31.

65

Figure 33. Plot of absorbance (data points) and theoretical absorbance (lines) versus pH for

titration of PDAM:TETREN:In (2x10-5

M).

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00

Ab

sorb

ance

pH

294 nm

294 nm Theoretical

284 nm

284 nm Theoretical

253 nm

253 nm Theoretical

237 nm

237 nm Theoretical

66


EXCEL in the determination of log K1 of PDAM:TETREN:In 1:1:1.


Standard

Deviation

log K1 9.43 0.004573

294 nm

Abs(0) 0.319

0.003392 Abs(1) 0.317

Abs(2) 0.539

284 nm

Abs(0) 0.412

0.006565 Abs(1) 0.485

Abs(2) 0.370

253 nm

Abs(0) 0.285

0.004712 Abs(1) 0.364

Abs(2) 0.480

237 nm

Abs(0) 0.754

0.003624 Abs(1) 0.737

Abs(2) 0.569

67

Uranyl (VI) Results

Uranyl is classified as a hard acid according to the HSAB principle. The UO22+

ion is of

particular interest because it is present in spent nuclear waste. This metal has a high affinity with

nitrogen donors because of its higher log K1 (NH3) of 2.0 which is higher than most metal ions.

A solution of 3.33 x 10-3

M UO2(ClO4)2 was added to 2x10-5

M PDAM with 0.1 M NaClO4.

The UV/Vis absorbance spectrum for UO22+

and PDAM is shown in Figure 34. A plot of the

corrected absorbance values versus log of the concentration of UO22+

is shown in Figure 35.

From the selected wavelengths of 297, 284, and 256 nm a log K1 of 4.33 was calculated from

Equations 2-7 using the process as described above. Table 12 outlines the solutions of each

parameter that was varied using SOLVER along with the standard deviation of each variable.

Theoretical and measured absorbances were plotted for each wavelength by minimizing the sum

of the squares using SOLVER. The program was also used to minimized all standard deviations

and determine the best possible log K1 value.

68


M) and UO2(0.003333 M) with 0.1 M NaClO4


69

Figure 35. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[UO2]

for titration of PDAM and UO2(NO3)2.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

-8.00 -7.00 -6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00

Ab

sorb

ance

log [UO2]

297 nm

297 nm Theoretical

284 nm

284 nm Theoretical

256 nm

256 nm Theoretical

70


EXCEL in the determination of log K1 of PDAM- UO2 complex.


Standard

Deviation

log K1 4.33 0.004503

297 nm abs L 0.290

0.004043 abs ML 0.398

284 nm abs L 0.478

0.007869 abs ML 0.321

256 nm abs L 0.225

0.004930 abs ML 0.437

71

Yttrium (III) Results

Yttrium (III) has an ionic radius of 0.90 Å which is close to the ideal 1.00 Å ionic radius

for the complexation of PDAM. Yttrium is classified according to the HSAB principle as a hard

acid. Although Y3+

is close to the ideal size for complexation with PDAM, the affinity with N-

donors with Y3+

are rather unfavorable as seen with the log K1 with NH3 to be 0.4.[16] A

solution of 0.003333 M Y(NO3)3 was added to 2 x 10-5

M PDAM with 0.1 M NaClO4. The

UV/Vis spectra plotting absorbance versus log of the concentration of Y(NO3)3 are show in

Figure 36. Absorbances were recorded at 297, 292, 284 nm. This experiment produced a

precipitate that obscured all wavelengths below 250 nm. Therefore, the predicted value for the

log K1 of yttrium could be slightly inaccurate because there were several wavelengths that could

have been used in the calculation for the determination log K1, but had to be omitted due to this

precipitate. Although there were few wavelengths that were recorded, the spectra produced an

isosbestic point which clearly indicates that the complex did indeed form from the metal addition

experiment. The theoretical and measured absorbances were plotted for every wavelength by

minimizing the sum of the squares as shown in Figure 37. SOLVER was used to minimize the

standard deviation so that a more accurate log K1 value can be calculated. Table 13 summarizes

the solutions of each parameter that was changed by SOLVER. The log K1 was calculated to be

3.45 by using Equations 2-7 in the process mentioned above.

72


M) and Y(0.003333 M) with 0.1 M NaClO4


73

Figure 37 . Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Y] for

titration of PDAM and Y(NO3)3.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

-8.00 -7.00 -6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00

Ab

sorb

ance

log [Y]

297 nm

297 nm Theoretical

292 nm

292 nm Theoretical

284 nm

284 nm Theoretical

74


EXCEL in the determination of log K1 of PDAM-Y complex.


Standard

Deviation

log K1 3.45 0.001581

297 nm abs L 0.319

0.001364 abs ML 0.464

292 nm abs L 0.417

0.002432 abs ML 0.625

284 nm abs L 0.533

0.000948 abs ML 0.485

75

Thorium (IV) results

Thorium (IV) has an ionic radius of 0.94 Å which is slightly smaller than the 1.0 Å

favored by PDAM. Thorium has a log K1 (NH3) of only 0.1 which means that thorium has a low

affinity for N-donors. The value of the stability constant for thorium is of particular interest

because it was only other actinide besides uranyl for which a log K1 could be calculated.

Thorium is classified as a hard acid in the HSAB rules. The UV absorbance spectrum for

0.003488 M thorium (IV) additions with PDAM at 2.00 x 10-5

M is show in Figure 38 below.

Absorbances were recorded at 297, 284, and 256 nm because wavelengths experienced the

largest change in absorbances. The spectra also produced three very distinct isosbestic points

which are indicative of complexation of the [Th(PDAM)]4+

complex. The theoretical and

measured absorbances were plotted for every wavelength by minimizing the sum of the squares

as shown in Figure 39. SOLVER was used to minimize the standard deviation so that a more

accurate log K1 value can be calculated. Table 14 summarizes the solutions of each parameter

that was changed by SOLVER. The log K1 was calculated to be 5.01 by using Equations 2-7 in

the process mentioned above. Because there is a slightly higher log K1 value than expected with

PDAM this could be explained for the slightly higher cationic charge on thorium which makes

up for its lack of affinity for nitrogen donors.

76


M) and Th(0.003488 M) with 0.1 M NaClO4


77

Figure 39 . Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Th] for

titration of PDAM and Th(NO3)4.

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0.500

-8.00 -7.00 -6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00

Ab

sorb

ance

log [Th]

297 nm

297 nm Theoretical

284 nm

284 nm Theoretical

256 nm

256 nm Theoretical

78


EXCEL in the determination of log K1 of PDAM-Th complex.


Standard

Deviation

log K1 5.01 0.004029

297 nm abs L 0.262

0.000509 abs ML 0.546

284 nm abs L 0.470

0.007750 abs ML 0.270

256 nm abs L 0.216

0.000954 abs ML 0.503

79

Cadmium (II) Results

Cadmium has an ionic radius of 0.95Å and is classified as a soft acid. PDAM found to be

very selective for cadmium because of its ideal size. A solution of 2.00x10-5

M PDAM solution

was prepared and 0.003333 M of Cd(ClO4)2 was added to the solution. This analysis as shown in

Figure 40 was unable to give an accurate log K1 because very little Cd(ClO4)2 was needed to

form the complex. A second experiment shown in Figure 41 was conducted by using 50.0 mL

solution of 1:1:1 PDAM: Cd(ClO4)2:EDTA at 2.00x10-5

M and was acidified to an initial pH of

2.20. This was titrated with 0.10 M NaOH solution to a final pH of 7.39. The UV/Vis spectra

plotting absorbance versus wavelength is shown in Figure 43. Absorbances were recorded at

330, 316, 287, 261, and 250 nm because these wavelengths exhibited the largest change in

absorbances. A log K1 of 7.05 was calculated from the absorbance data using the process as

described above. Theoretical and measured absorbances were plotted for each wavelength by

minimizing the sum of the squares using SOLVER. Table 15 summarizes the solutions of each

parameter that was changed by SOLVER. The program was also used to minimized all standard

deviations and determine the best possible log K1 value.

Cadmium has higher stability with PDAM than most of the other metal ions analyzed.

The reasoning for its high log K1 value is that it is at an ideal size and can bind to all four donor

atoms unlike 1, 10-phenanthroline with a log K1 of 5.66. However, denticity and preorganization

are the primary factors for the high stability of the [Cd(PDAM)]2+

complex.

To further justify the log K1 of cadmium with PDAM another experiment shown in

Figure 42 and 44 was performed in competition with TETREN. Table 16 summarizes the

80

solutions of each parameter that was changed by SOLVER. The log K1 value for cadmium was

calculated to be 7.04.


M) and Cd (0.003230M) with 0.1 M NaClO4


81

Figure 41. UV/Vis spectra of PDAM:Cd(ClO4)2:EDTA 1:1:1 at (2x10-5

M) and 0.1 M NaClO4

present. Initial at pH 2.20 to a final pH of 7.39.

82

Figure 42. UV/Vis spectra of PDAM:Cd(ClO4)2:TETREN 1:1:1 at (2x10-5

M) and 0.1 NaClO4

present. Initial at pH 2.44 to a final pH of 9.49.

83

Figure 43. Plot of corrected absorbance (data points) and theoretical absorbance (lines) versus

pH for titration of 1:1:1 PDAM:Cd(ClO4)2:EDTA.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.00 2.00 4.00 6.00 8.00 10.00

Ab

sorb

ance

pH

290 nm

290 nm Theoretical

252 nm

252 nm Theoretical

231 nm

231 nm Theoretical

212 nm

212 nm Theoretical

84

Figure 44. Plot of corrected absorbance (data points) and theoretical absorbance (lines) versus

pH for titration of 1:1:1 PDAM:Cd(ClO4)2:TETREN.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.00 2.00 4.00 6.00 8.00 10.00

Ab

sorb

ance

pH

288 nm

288 nm Theoretical

284 nm

284 nm Theoretical

250 nm

250 nm Theoretical

236 nm

236 nm Theoretical

85


EXCEL in the determination of log K1 of PDAM:EDTA:Cd 1:1:1 complex.


Standard

Deviation

log K1 7.05 0.01509

290 nm

Abs(0) 0.074

0.018557 Abs(1) 0.138

Abs(2) 0.173

252 nm

Abs(0) 0.000

0.011507 Abs(1) 0.170

Abs(2) 0.201

231 nm

Abs(0) 0.140

0.017782 Abs(1) 0.325

Abs(2) 0.360

212 nm

Abs(0) 1.923

0.012498 Abs(1) 0.467

Abs(2) 0.468


EXCEL in the determination of log K1 of PDAM:TETREN:Cd 1:1:1 complex.


Standard

Deviation

log K1 7.04 0.002471

288 nm

Abs(0) 0.416

0.003522 Abs(1) 0.508

Abs(2) 0.519

284 nm

Abs(0) 0.448

0.001510 Abs(1) 0.489

Abs(2) 0.484

250 nm

Abs(0) 0.467

0.001891 Abs(1) 0.493

Abs(2) 0.495

236 nm

Abs(0) 0.705

0.005016 Abs(1) 0.661

Abs(2) 0.660

86

Calcium(II)-PDAM results

Calcium has an ionic radius of 1.00 Å which is the most ideal size for PDAM. Calcium is

classified according to the HSAB principle as a hard acid. Although calcium possesses the

correct ionic radius for the complexation of PDAM, previous studies [11,17-19,22] have shown

calcium to have low affinity for nitrogen donors. A solution of 1.0 M Ca(ClO4)2 was added to

2 x 10-5

M PDAM with 0.1M NaClO4. The UV/Vis spectra plotting absorbance versus log of the

concentration of Ca(ClO4)2 are show in Figure 45. Absorbances were recorded at 316, 287, 283,

251, 248, 235, 209 nm. The theoretical and measured absorbances were plotted for every

wavelength by minimizing the sum of the squares as shown in Figure 46. SOLVER was used to

minimize the standard deviation so that a more accurate log K1 value can be calculated. Table 17

summarizes the solutions of each parameter that was changed by SOLVER. The log K1 was

calculated to be 1.94 by using Equations 2-7 in the process mentioned above.

87


M) and Ca(ClO4)2 (1.0 M) with 0.1 NaClO4 present.

Initial pH 5.37.

88

Figure 46. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Ca] for

titration of PDAM and Ca(ClO4)2.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

-6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00

Ab

sorb

ance

log [Ca]

316 nm

316 nm Theoretical

287 nm

287 nm Theoretical

283 nm

283 nm Theoretical

251 nm

251 nm Theoretical

248 nm

248 nm Theoretical

235 nm

235 nm Theoretical

209 nm

209 nm Theoretical

89


EXCEL in the determination of log K1 of PDAM-Ca complex.


Standard

Deviation

log K1 1.94 0.0035581

316 nm abs L 0.175

0.000699 abs ML 0.192

287 nm abs L 0.521

0.002133 abs ML 0.636

283 nm abs L 0.556

0.001955 abs ML 0.581

251 nm abs L 0.489

0.004471 abs ML 0.560

248 nm abs L 0.583

0.004304 abs ML 0.574

235 nm abs L 0.831

0.004819 abs ML 0.742

209 nm abs L 0.534

0.006527 abs ML 0.564

90

Bismuth (III) Results

Bismuth has an ionic radius of 1.03Å and is classified as an intermediate acid according

to the HSAB principle. This is an ideal metal ion because it has a high affinity with nitrogen

donors. Bismuth also contains a large peak sharpening at 250 nm which is characteristic of

PDAM forming a complex with large metal ions. Because the metal ion binds so well with

PDAM, that like indium, metal addition would not be able to accurately determine the log K1

value of bismuth with PDAM. Therefore, a competition reaction with TETREN was used to

determine a more accurate value of log K1. This experiment was conducted by using 50.0 mL

solution of 1:1:1 PDAM: Bi(NO3)3:TETREN at 2.00x10-5

M and was acidified to an initial pH of

2.10. This was titrated with 0.10 M NaOH solution to a final pH of 7.11. The UV/Vis spectra

plotting absorbance versus wavelength is shown in Figure 47. Absorbances were recorded at

298, 284, and 255 nm because these wavelengths exhibited the largest change in absorbances.

The theoretical and measured absorbances were plotted for every wavelength by minimizing the

sum of the squares as shown in Figure 48. A log K1 of 9.44 was calculated from the absorbance

data using the process as described above. Table 18 summarizes the solutions of each parameter

that was changed by SOLVER. The program was also used to minimized all standard deviations

and determine the best possible log K1 value.

91

Figure 47. UV/Vis spectra of PDAM:TETREN:Bi (2x10-5

M) with 0.1 NaClO4 present. Initial

pH at 2.10 to a final pH of 7.11.

92


titration of PDAM:TETREN:Bi(2x10-5

M).

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00

Ab

sorb

ance

pH

298 nm

298 nm Theoretical

284 nm

284 nm Theoretical

255 nm

255 nm Theoretical

93


EXCEL in the determination of log K1 of PDAM:TETREN:Bi 1:1:1 complex.


Standard

Deviation

log K1 9.44 0.004304

336 nm

Abs(0) 0.046

0.000785 Abs(1) 0.039

Abs(2) 0.106

298 nm

Abs(0) 0.254

0.004625 Abs(1) 0.284

Abs(2) 0.475

284 nm

Abs(0) 0.532

0.006224 Abs(1) 0.495

Abs(2) 0.306

255 nm

Abs(0) 0.340

0.005584 Abs(1) 0.307

Abs(2) 0.503

94

Lead (II) results

Lead has an ionic radius of 1.19Å and is the largest metal ion studied with PDAM. Lead

is an intermediate acid according to the HSAB principle. Intermediate acids are expected to bind

preferably well with nitrogen donor groups. The first metal addition study showed that a very

dilute addition of Pb(ClO4)2 to PDAM complexed almost immediately to form [Pb(PDAM)]2+

complex. Therefore, another experiment was needed in order to accurately calculate the log K1 of

lead with PDAM. A competition reaction with TETREN was performed with PDAM and lead at

a ratio of 1:1:1. A solution of PDAM, TETREN, and Pb(ClO4)2 was titrated with 0.1 M NaOH

from an initial pH=2.27 to a final pH=8.11. The UV/Vis spectra plotting absorbance versus

wavelength is shown in Figure 49. Absorbances were recorded at 292, 284, 249, and 237 nm

because these wavelengths displayed the largest change in absorbances. The theoretical and

measured absorbances were plotted for these wavelengths mentioned above simultaneously by

minimized the standard deviation using SOLVER to determine a more accurate log K1 value as

shown in Figure 50. Table 19 summarizes the solutions of each parameter that was changed by

SOLVER. The log K1 was calculated to be 5.82 by using Equations 2-7 in the process

mentioned above. Although PDAM is selective for large metal ions around 1.00 Å, lead(II) as

shown in this experiment was too large to form a stable complex. This could be due to steric

hindrance with the amides which causes the conditions for complexation to become unfavorable.

95

;

Figure 49. UV/Vis spectra of PDAM :TETREN:Pb 1:1:1 at (2x10-5

M) with 0.1 NaClO4 present.

Initial pH at 2.27 to final pH of 8.11.

96


titration of PDAM:TETREN:Pb 1:1:1.

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0.00 2.00 4.00 6.00 8.00 10.00

Ab

sorb

ance

pH

292 nm

292 nm Theoretical

284 nm

284 nm Theoretical

249 nm

249 nm Theoretical

237 nm

237 nm Theoretical

97


EXCEL in the determination of log K1 of PDAM:TETREN:Pb 1:1:1 complex.


Standard

Deviation

log K1 5.82 0.001588

292 nm

Abs(0) 0.177

0.001000 Abs(1) 0.172

Abs(2) 0.234

284 nm

Abs(0) 0.251

0.001288 Abs(1) 0.252

Abs(2) 0.213

249 nm

Abs(0) 0.309

0.001829 Abs(1) 0.316

Abs(2) 0.254

237 nm

Abs(0) 0.405

0.002234 Abs(1) 0.415

Abs(2) 0.308

98

Lanthanide Results

In Figures 54-67 are the spectra of the lanthanide series except for promethium because it

is radioactive and cannot be experimented at this facility. The preparation of the lanthanides

consisted of 2 x 10-5

M PDAM solution in 0.1 M NaClO4 with the addition of 3x10-3

M of Ln3+

concentration held at their initial pH which ranged from 2-5 to prevent hydrolysis. These spectra

have clear isosbestic points which indicate the formation of the [Ln(PDAM)]3+

complex at a

single equilibrium. In Figures 68-81 show the variation of absorbance as a function of the

logarithm of the Ln(III) concentration at several wavelengths because these wavelengths

displayed the largest change in absorbances. The midpoints in the inflections of these curves give

the value of the log K1 of PDAM. The calculated theoretical and measured absorbances were

fitted for these wavelengths mentioned above simultaneously. This fit was performed to

minimize the standard deviation using SOLVER to determine a more accurate log K1 value.

Tables 21-34 summarize the solutions of each parameter in the lanthanide series that was

changed by SOLVER. The UV spectrum of PDAM and its response to the formation of

complexes with metal ions is quite similar to that of PDA[11,17,27]. The lanthanide series of

PDAM was analyzed and compared to PDA’s log K1 values. By comparing log K1 values of the

lanthanide metals a similarity arose in that when a formation of a complex occurred with a large

metal ion of an ionic radius close to 1.0 Å a sharp peak appears. This occurred with PDAM at

253 nm, and for PDA it occurred at 247 nm. These sharp peaks that appears upon the formation

of the complex has been suggested [17,27] to be due to the vibrations coupled to the π-π*

transitions of the ligand.

99


M) and Ce(0.003333 M) with 0.1 NaClO4 present.

Note the sharp band at 250 nm, which appears upon the binding Ce(III) to all four donor groups

of PDAM.

The log K1 results on Table 20 demonstrate that PDAM has a relatively high affinity for

the lanthanide series as predicted by its relative ligand, PDA. The lanthanide ions average log K1

has shown an overall value 4.0. The amide oxygen donors of PDAM when compared to phen

alone dramatically stabilize the log K1 for the lanthanide series by about 3 log units [27]. These

amide oxygen donors of PDAM turn phen from a very weak ligand with lanthanide ions into a

decently strong ligand. By increasing the log K1 of the lanthanides, this gives evidence to the fact

that PDAM could be a particularly great candidate as a solvent extractant.

The small deviation in the log K1 values in going across the series of lanthanide ions from

La(III) to Lu(III) is very interesting and useful for PDAM as a possible solvent extractant. In

Figure 52 shows a comparison [26] in the log K1 values of the lanthanide series of PDAM with

other aminopolycarboxylate ligands.

100

Figure 52. Plot of change in log K1 for a variety of ligands relative to the La(III) complex for

Ln(III) ions plotted as a function of the number of f-electrons. Log K1 data ionic strength 0.1, 25

°C. [26]

101

Figure 53. Comparison of ionic radii for the Ln(III) ions in angstroms.

In particular interest is the comparison between PDAM and EDDA which is also a tetradentate

ligand. It too shows a larger increase in log K1 in passing from La(III) to Lu(III) than PDAM. .

The main reason for the large changes in the log K1 values for the other ligands across the

lanthanide series is due to steric crowding. This is the explanation for the little change in log K1

from Gd(III) to Lu(III) in octadentate ligands, DTPA and DOTA. The metal ion size decreases

when going across the lanthanide series which has coined the term lanthanide contraction as

shown in Figure 53. Therefore, when going from Gd(III) to Lu (III) there is an increase in steric

crowding because the size of the metal ion decreases. Ionic radii can also explain why the

0.8

0.85

0.9

0.95

1

1.05

1.1

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

1.05

1.02

0.990 0.983

0.9580.947

0.9380.923

0.9120.901

0.8900.880

0.868 0.861

Ion

ic R

adiu

s (Å

)

Lanthanides (III)

102

hexadentate CDTA and EDTA have a sharp rise in log K1 from Gd(III) to Lu(III) because there

is less steric crowding during the complexation.

For PDAM, the factor governing complex stability is the affinity of the neutral oxygen

donor[13] has for larger metal ions. In this case, the larger metal ions in the lanthanide series

profit the most from the presence of the neutral oxygen donors, which in turn offsets the ability

of the smaller lanthanide ions to form stronger bonds with the nitrogen donors in PDAM.

Nitrogen donors are also an important aspect in determining the affinity of metal ions have on a

ligand. To determine which ions have the most affinity to nitrogen donors the log K1 (NH3)

values were predicted [16] from DFT calculations on Table 2. These calculations show that

there is a great affinity with the actinide cations Am3+

, Pu4+

, and the UO22+

cation for NH3 which

is related to the affinity of the nitrogen donor atom. Predicting which metal ions have strong

affinities for nitrogen donors can prove to be a useful tool in designing ligands for metal ion

separations.

103

Table 20. Protonation and formation constants for the lanthanide(III) series with PDAM

determined in 0.1 M NaClO4 at 25 ºC. (L = PDAM in given equilibria).

________________________________________________________________________

Equilibrium log K Ionic Radius(Å)

________________________________________________________________________

La3+

+ L = LaL3+

3.80 1.05

Ce3+

+ L = CeL3+

4.06 1.02

Pr3+

+ L = PrL3+

4.09 0.99

Nd3+

+ L = NdL3+

4.09 0.98

Sm3+

+ L = SmL3+

4.27 0.96

Eu3+

+ L = EuL3+

4.17 0.95

Gd3+

+ L = GdL3+

4.30 0.94

Tb3+

+ L = TbL3+

3.93 0.92

Dy3+

+ L = DyL3+

4.05 0.91

Ho3+

+ L = HoL3+

3.89 0.90

Er3+

+ L = ErL3+

3.84 0.89

Tm3+

+ L = TmL3+

3.88 0.88

Yb3+

+ L = YbL3+

4.08 0.87

104

Lu3+

+ L = LuL3+

3.80 0.86

________________________________________________________________________


M) and La (0.003333 M) with 0.1 NaClO4 present.

Initial pH at 5.46.

105


M) and Ce(0.003333 M) with 0.1 NaClO4 present.

Initial pH at 4.70.


M) and Pr(0.003402 M) with 0.1 NaClO4 present.

Initial pH at 2.27.

106


M) and Nd(0.003385 M) with 0.1 NaClO4 present.

Initial pH at 2.12.


M) and Sm(0.003505 M) with 0.1 NaClO4 present.

Initial pH at 2.25.

107


M) and Eu(0.003360 M) with 0.1 NaClO4 present.

Initial pH at 2.17.


M) and Gd (0.003333M) with 0.1 NaClO4 present.

Initial pH at 4.18.

108


M) and Tb(0.003557 M) with 0.1 NaClO4 present.

Initial pH at 2.28.


M) and Dy(0.003557 M) with 0.1 NaClO4 present.

Initial pH at 2.16.

109


M) and Ho(0.003271 M) with 0.1 NaClO4 present.

Initial pH at 2.20.


M) and Er(0.003354 M) with 0.1 NaClO4 present.

Initial pH at 2.22.

110


M) and Tm(0.003343 M) with 0.1 NaClO4 present.

Initial pH at 2.23.


M) and Yb(0.003333 M) with 0.1 NaClO4 present.

Initial pH at 5.51.

111


M) and Lu (0.003333M) with 0.1 NaClO4 present.

Initial pH at 4.15.

112

Figure 68. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[La] for

titration of PDAM and La(ClO4)3.

Figure 69. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Ce] for

titration of PDAM and Ce(ClO4)4.

0.480

0.490

0.500

0.510

0.520

0.530

0.540

0.550

0.560

0.570

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [La]

292 nm

292 nm Theoretical

289nm

289 nm Theoretical

0.000

0.100

0.200

0.300

0.400

0.500

0.600

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Ce]

331 nm

331 theoretical

292 nm

292 nm theoretical

283 nm

283 nm theoretical

113

Figure 70. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Pr] for

titration of PDAM and Pr(ClO4)3.

Figure 71. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Nd] for

titration of PDAM and Nd(ClO4)3.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Pr]

292 nm

292 nm Theoretical

284 nm

284 nm Theoretical

253 nm

253 nm Theoretical

236 nm

236 nm Theoretical

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Nd]

292 nm

292 Theoretical

284 nm

284 nm Theoretical

253 nm

253 Theoretical

236 nm

236 nm Theoretical

114

Figure 72. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Sm] for

titration of PDAM and Sm(ClO4)3.

Figure 73. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Eu] for

titration of PDAM and Eu(OSO2CF3)3.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Sm]

292 nm

292 nm Theoretical

284 nm

284 nm Theoretical

253 nm

253 nm Theoretical

236 nm

236 nm Theoretical

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Eu]

292 nm

292 nm Theoretical

284 nm

284 nm Theoretical

253 nm

253 nm Theoretical

236 nm

236 nm Theoretical

115

Figure 74. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Gd] for

titration of PDAM and Gd(ClO4) 3.

Figure 75. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Tb] for

titration of PDAM and Tb(ClO4)3.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Gd]

292 nm

292 nm Theoretical

289 nm

289 nm Theoretical

282 nm

282 nm Theoretical

248 nm

248 nm Theoretical

235 nm

235 nm Theoretical

222 nm

222 nm Theoretical

217 nm

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Tb]

292 nm

292 nm Theoretical

284 nm

284 nm Theoretical

253 nm

253 nm Theoretical

236 nm

236 nm Theoretical

116

Figure 76. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Dy] for

titration of PDAM and Dy(ClO4)3.

Figure 77. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Ho] for

titration of PDAM and Ho(ClO4)3.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

1.000

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Dy]

292 nm

292 nm Theoretical

284 nm

284 nm Theoretical

253 nm

253 nm Theoretical

236 nm

236 nm Theoretical

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Ho]

292 nm

292 nm Theoretical

284 nm

284 nm Theoretical

253 nm

253 nm Theoretical

236 nm

236 nm Theoretical

117

Figure 78. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Er] for

titration of PDAM and Er(ClO4)3.

Figure 79. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Tm] for

titration of PDAM and Tm(CF3SO3)3.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Er]

292 nm

292 nm Theoretical

284 nm

284 nm Theoretical

253 nm

253 nm Theoretical

236 nm

236 nm Theoretical

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log[Tm]

292 nm

292 nm Theoretical

284 nm

284 nm Theoretical

253 nm

253 nm Theoretical

236 nm

236 nm Theoretical

118

Figure 80. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Yb] for

titration of PDAM and Yb(NO3)3.

Figure 81. Plot of absorbance (data points) and theoretical absorbance (lines) versus log[Lu] for

titration of PDAM and Lu(ClO4)3.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Yb]

292 nm

292 nm Theoretical

289 nm

289 nm Theoretical

282 nm

282 nm Theoretical

248 nm

248 nm Theoretical

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

-8.00 -6.00 -4.00 -2.00 0.00

Ab

sorb

ance

log [Lu]

292nm

292 nm Theoretical

289 nm

289 nm Theoretical

282 nm

282 nm Theoretical

255 nm

255 nm Theoretical

248 nm

248 nm Theoretical

235 nm

235 theoretical

222 nm

119


EXCEL in the determination of log K1 of PDAM-La complex.


Standard

Deviation

log K1 3.80 0.001705

297 nm abs L 0.489

0.001830 abs ML 0.582

284 nm abs L 0.562

0.001580 abs ML 0.468


EXCEL in the determination of log K1 of PDAM-Ce complex.


Standard

Deviation

log K1 4.06 0.002639

331nm abs L 0.113

0.000737 abs ML 0.148

292nm abs L 0.377

0.005069 abs ML 0.557

283 nm abs L 0.500

0.002113 abs ML 0.446


EXCEL in the determination of log K1 of PDAM-Pr complex.


Standard

Deviation

log K1 4.09 0.002819

292 nm abs L 0.372

0.003665 abs ML 0.537

284 nm abs L 0.467

0.002992 abs ML 0.415

253 nm abs L 0.357

0.003025 abs ML 0.477

236 nm abs L 0.700

0.001593 abs ML 0.582

120


EXCEL in the determination of log K1 of PDAM-Nd complex.


Standard

Deviation

log K1 4.01 0.007808

292 nm abs L 0.378

0.006496 abs ML 0.610

284 nm abs L 0.484

0.008339 abs ML 0.446

253 nm abs L 0.360

0.003025 abs ML 0.530

236 nm abs L 0.725

0.011120 abs ML 0.623


EXCEL in the determination of log K1 of PDAM-Sm complex.


Standard

Deviation

log K1 4.27 0.005048

292 nm abs L 0.369

0.004691 abs ML 0.588

284 nm abs L 0.486

0.005428 abs ML 0.435

253 nm abs L 0.344

0.003948 abs ML 0.509

236 nm abs L 0.730

0.006127 abs ML 0.612

121


EXCEL in the determination of log K1 of PDAM-Eu complex.


Standard

Deviation

log K1 4.17 0.006901

292 nm abs L 0.365

0.004667 abs ML 0.569

284 nm abs L 0.470

0.005649 abs ML 0.419

253 nm abs L 0.344

0.004526 abs ML 0.500

236 nm abs L 0.710

0.007903 abs ML 0.606


EXCEL in the determination of log K1 of PDAM-Gd complex.


Standard

Deviation

log K1 4.38 0.006725

292 nm abs L 0.349

0.016545 abs ML 0.509

289 nm abs L 0.425

0.011529 abs ML 0.483

282 nm abs L 0.486

0.002193 abs ML 0.364

248 nm abs L 0.526

0.007075 abs ML 0.477

235 nm abs L 0.731

0.001893 abs ML 0.556

222 nm abs L 0.506

0.002805 abs ML 0.467

217 nm abs L 0.439

0.005890 abs ML 0.472

204 nm abs L 0.462

0.005870 abs ML 0.451

122


EXCEL in the determination of log K1 of PDAM-Tb complex.


Standard

Deviation

log K1 3.93 0.005074

292 nm abs L 0.364

0.003471 abs ML 0.583

284 nm abs L 0.473

0.005170 abs ML 0.434

253 nm abs L 0.340

0.004555 abs ML 0.507

236 nm abs L 0.708

0.007100 abs ML 0.603


EXCEL in the determination of log K1 of PDAM-Dy complex.


Standard

Deviation

log K1 4.05 0.006206

292 nm abs L 0.442

0.003854 abs ML 0.651

284 nm abs L 0.587

0.005738 abs ML 0.499

253 nm abs L 0.409

0.005167 abs ML 0.562

236 nm abs L 0.874

0.007352 abs ML 0.691

123


EXCEL in the determination of log K1 of PDAM-Ho complex.


Standard

Deviation

log K1 3.89 0.002338

292 nm abs L 0.373

0.001212 abs ML 0.574

284 nm abs L 0.489

0.000480 abs ML 0.433

253 nm abs L 0.348

0.004704 abs ML 0.491

236 nm abs L 0.733

0.002955 abs ML 0.598


EXCEL in the determination of log K1 of PDAM-Er complex.


Standard

Deviation

log K1 3.84 0.003352

292 nm abs L 0.391

0.003597 abs ML 0.615

284 nm abs L 0.509

0.001576 abs ML 0.464

253 nm abs L 0.358

0.006543 abs ML 0.523

236 nm abs L 0.755

0.001691 abs ML 0.628

124


EXCEL in the determination of log K1 of PDAM-Tm complex.


Standard

Deviation

log K1 3.88 0.004818

292 nm abs L 0.370

0.006333 abs ML 0.576

284 nm abs L 0.472

0.003132 abs ML 0.442

253 nm abs L 0.338

0.007257 abs ML 0.486

236 nm abs L 0.696

0.002550 abs ML 0.596


EXCEL in the determination of log K1 of PDAM-Yb complex.


Standard

Deviation

log K1 4.08 0.003796

292 nm abs L 0.420

0.004341 abs ML 0.660

289 nm abs L 0.496

0.003934 abs ML 0.620

282 nm abs L 0.558

0.001985 abs ML 0.447

248 nm abs L 0.602

0.004923 abs ML 0.586

125


EXCEL in the determination of log K1 of PDAM-Lu complex.


Standard

Deviation

log K1 3.80 0.007767

292 nm abs L 0.354

0.006258 abs ML 0.631

289 nm abs L 0.420

0.006642 abs ML 0.584

282 nm abs L 0.477

0.007619 abs ML 0.409

255 nm abs L 0.263

0.004631 abs ML 0.537

248 nm abs L 0.522

0.007525 abs ML 0.527

235 nm abs L 0.729

0.010318 abs ML 0.603

222 nm abs L 0.509

0.006485 abs ML 0.539

217 nm abs L 0.443

0.007304 abs ML 0.561

204 nm abs L 0.463

0.013124 abs ML 0.524

126

Fluorescence Results

The study of fluorescence on 1, 10 phen-based ligands have shown remarkable

fluorescence properties [18,27] in aqueous solution. By studying the fluorescence of PDAM we

may be able to observe CHEF (chelation enhanced fluorescence) effects, which can be useful in

sensing metal ions [28,29,30]. PDAM proved to be a great candidate for fluorescence because it

fluoresces strongly as the free ligand. The reason it fluoresces so strongly is due to the rigidness

of the ligand as well as the conjugation of the 1,10-phen backbone. The free ligand has a strong

emission at 365 nm when excited at 250 nm. The concentration of the free ligand was 2x10-5

M,

which is useful in the detection metal ions at a minimal concentration.

There are three factors that control the CHEF effect with metal ions [31]. First, is the

presence of unpaired electrons, like Cu(II) or Gd(II) which quench fluorescence. Second, heavy

atoms like Pb, Hg, or I directly and covalently to the fluorophore. These heavy atoms quenches

fluorescence because of spin-orbit coupling effects. The final factor that controls the CHEF

effect is metal ions that are lighter (Zn (II) or Ca(II)) or heavier ions such as Lu (III) that bind

ionically to the fluorophores which produce a positive CHEF effect. This increases fluorescence

intensity according to the amount of formation of the complex.

In Figure 83 shows a spectra of PDAM as the free ligand. It is intresting to see that

PDAM does fluoresce strongly, however upon the addition of the metal ion is gradually

quenched by the increase in metal ion concentration as seen in Figures 84-90. In previous studies

[18,27], have shown that metal ions like Zn(II) and Ca(II) produce strong positive CHEF effects.

This behavior can only be explained by the the resonance of PDAM is increased when binding to

a metal ion as shown in Figure 82 below.

127

NN

H2NC CNH2

O O

NN

CNH2OO

M+

M

+H2N

Figure 82. Resonance of PDAM when bound to a metal, (M).

As illustrated in Figure 82, the quenching for all metal ions comes from this particular

configuration in which there is a positive charge on the nitrogen ion from the amide group. This

configuration causes quenching to occur and shows a negative CHEF effect for all metal ions

when the concentration is increased. Otherwise, the behavior of PDAM cannot be explained by

the terms of the three factors [27] that control the CHEF effect.

128

Figure 83. Fluorescence spectrum of 2x10-5

M PDAM as a function of emission intensity (a.u.)

versus wavelength (nm). Excitation wavelength = 250 nm.

0.00E+00

1.00E+07

2.00E+07

3.00E+07

4.00E+07

5.00E+07

6.00E+07

7.00E+07

335 355 375 395 415 435

em

issi

on

inte

nsi

ty (

a.u

.)

wavelength (nm)

free PDAM

129

Figure 84. Fluorescence spectra of 2x10-5

M PDAM as a function of Zn(II) concentration,

indicated at right in exponent-form notation. Excitation wavelength = 250 nm.

130


M PDAM as a function of Gd(II) concentration,


131


M PDAM as a function of Cd(II) concentration,


132


M PDAM as a function of Sc(III) concentration,


133


M PDAM as a function of La(III) concentration,


134


M PDAM as a function of Pb(II) concentration,


135


M PDAM as a function of Lu(III) concentration,


136

PDAM Degradation Experiment Results

The purpose of a degradation experiment was to test the stability of PDAM towards

hydrolysis in strong acid. A solution of PDAM was acidified with 1.0 M HClO4 and analyzed

several times over a seven month period. After three months it was found that only a small shift

in the 200 nm base-line region occurred in the UV/Vis spectrum. This effect is usually related

with light-scattering caused by the formation of a minute amount of precipitate. This precipitate

is most likely due to the perchlorate salt of PDAM. These results are of particular importance

because the current extraction processes are conducted under very acidic conditions in which

there is basically a competition of coordination to the ligand between the proton and the An(III)

ion. The low protonation constant, due to the electron withdrawing nature of the amide groups

effect on the N-donors of the phen backbone, allows PDAM to resist hydrolysis for long periods

of time.

137

Figure 91. UV/Vis spectra of PDAM degradation experiment.

138

Molecular Mechanics Calculations

The best-fit size of metal ions for the coordination to PDAM was analyzed by using MM

calculations. The M–N and M–O bond lengths were varied systematically in 0.1 Å increments

between M–N values of 2.0 to 3.0 Å while keeping the M–N force constant at a value of 0.7

mdyne/Å. The ideal M–O bond length was put at a constant 0.05 Å shorter that the M–N bond

length to achieve the ideal M–O bond length for each point in the calculation. This difference of

0.05 Å is due to the difference in size between the N and O atoms. The curve of U (strain energy)

versus M–N length was produced by MM for the complex [M(PDAM)(H2O)2]3+

is seen in Figure

92. The polynomial equation in Figure 92 determines the best-fit size of the metal ion by

calculating the M–N bond length that produced the minimum strain energy of the curve. The

minimum in U for these complexes occurs with M–N= 2.52 Å, which is equal to the best-fit size

of metal ion for the coordination with PDAM. This would allow selectivity against metal ions

that that cannot achieve M–O lengths of close to half this distance which would be 2.41 Å. The

structure of [Y(PDAM)(NO3)3] was predicted as seen in Figure 93.

139

Figure 92. The polynomial equation of strain energy (U) for [M(PDAM)(H2O)2]3+

as a function

of M–N bond length determined by MM calculations.

140

Figure 93. Predicted structure of [Y(PDAM)(NO3)3] through MM calculations.

141

CONCLUSIONS

The ligand 1,10-phenanthroline-2,9-dicarboxamide, (PDAM) shows great promise as an

solvent extractant for the separation of spent nuclear waste. The method of ligand design as a

means to create a highly selective ligand has proven to be successful. This ability to have

PDAM selectively bind to a specific metal ion in solution is of great importance in nuclear

industry. The qualities in ligand design such as the strong 1,10 phen backbone to aid in

preorganization, chelate rings size, amide groups which aid in donor atom selection, and rigidity

all facilitate in the complexation of a metal ion that possesses a large ionic radius and higher

charge.

PDAM was synthesized according to the literature method with moderate changes in

overall reaction times. This ligand was confirmed by the characterization of NMR and IR and

UV spectroscopy. By the utilization of the UV/Vis absorption spectroscopy the detection of the

complexation of metals in solution as a function of concentration was concluded to be a

successful method.

PDAM shows a reasonably strong size-based selectivity in that the log K1 values of the

PDAM complexes of Ni(II) and Zn(II) are small values with log K1=3.06 and 3.77 respectively.

The somewhat larger metal ions like In(III), Bi(III), and Cd(II) all have a very high log K1

values. The sharp band at 250 nm in the electronic spectra of the PDAM complexes appears to be

a good indicator of whether the metal is able to coordinate with all four donor atoms of PDAM

simultaneously.

PDAM complexes of the lanthanides have shown to have a small deviation in log K1 in

passing from La(III) to Lu(III) averaging a log K1 = 4.0. The small change in formation constants

142

is explained in terms of the idea that neutral O-donors stabilize the complexes of the large La(III)

ion more than the smaller Lu(III) ion, offsetting the greater affinity of Lu(III) than La(III) for N-

donor ligands.

The very low proton affinity of PDAM is also an important factor in extracting metal ions

from acidic solutions as shown in the degradation experiment. The fluorescent properties of

PDAM may also prove to be useful in monitoring metal ion extraction.

143

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