PHOSPHATE HYBRID-FRAMEWORK MATERIALS By YUE ZHAO … · 2013. 5. 8. · new MOP materials with novel structures. They show a great diversity of structural topologies, coordination

PREPARATION AND INVESTIGATION OF GROUP 13 METAL ORGANO-

PHOSPHATE HYBRID-FRAMEWORK MATERIALS

By

YUE ZHAO

A Dissertation Submitted to the Graduate Faculty of

WAKE FOREST UNIVERSITY GRADUATE SCHOOL OF ARTS AND SCIENCES

in Partial Fulfillment of the Requirements

for the Degree of

DOCTOR OF PHILOSOPHY

In the Department of Chemistry

May 2009

Winston-Salem, North Carolina

Copyright by Yue Zhao 2009

Approved by:

Abdessadek Lachgar, Ph. D., Advisor _____________________________

Examining Committee:

Natalie A. W. Holzwarth, Ph. D., Chair _____________________________

Christa L. Colyer, Ph. D. _____________________________

Bradley T. Jones, Ph. D. _____________________________

Ronald E. Noftle, Ph. D. _____________________________

I

ABSTRACT

Preparation and Investigation of Group 13 Metal Organo-Phosphate Hybrid-Framework

Materials

by

Yue Zhao

Dissertation under the direction of Abdessadek Lachgar,

Ph.D., Professor of Chemistry

Open-framework materials such as zeolites and low-dimensional materials such as

metal phosphates have a wide range of applications in separation processes, catalysis, ion

exchange, and intercalation chemistry. Current research in this field is focused on

synthesizing hybrid inorganic-organic compounds, which combine inorganic species as

nodes and organic species as linkers. These materials have been demonstrated to have

versatile structures and show promising properties for applications in the areas of

separation, catalysis, magnetism, photo-physics, and electronics.

The controlled synthesis of these materials is an ongoing challenge that offers

tremendous opportunities in the area of materials science. The objective of the research

conducted within the framework of this dissertation is to prepare and characterize hybrid

framework metal organo-phosphate materials (MOPs). The idea is to use specific

building units that can be linked or modified by functional organic groups to make

materials with specific architectures and thus specific properties. The objective is to reach

an understanding of how the organic and inorganic pieces fit together to allow for the

II

preparation of tailor-made materials with specific structures and specific functionality of

this type of materials.

The synthetic method of choice is a mild hydro- or solvo-thermal method in which

the reactants and solvent are sealed in a container and heated slightly above the boiling

point of the solvent under autogeneous pressure. Their structural characterization was

done by single crystal X-ray diffraction. The presence of the organic moieties was

determined by the combination of elemental analysis, XRD and IR spectroscopy. The

thermal stability of these materials was determined by a combination of

thermogravimetric analysis, IR spectroscopy, and powder XRD.

The study has led to the preparation and complete characterization of a number of

new MOP materials with novel structures. They show a great diversity of structural

topologies, coordination types, dimensionalities, pore sizes and physical or chemical

properties. The MOPs synthesized and characterized can be classified in three different

types of hybrid frameworks:

(1) Hybrid frameworks built of pure inorganic metal phosphates (MPO4) layer or

chains linked or coordinated by multitopic organic ligands such as oxalate, 1,10 –

phenanthroline and 4,4’-bipyridine.

(2) Hybrid frameworks built of metal phosphonates (MPO3R) or metal

diphosphonates (MPO3RPO3). In this case the organic functional group is embedded in

the inorganic framework.

(3) Hybrid frameworks that can be considered to be a combination of the previous

two types. They are built of metal phosphonate (MPO3R) layers or chains linked or

coordinated by multitopic organic ligands.

III

DEDICATION

To my parents, Tianhua Zhao and Yujun Fang

To my wife, Zhihua Yan

To my son, Yanxin Matthew Zhao

IV

ACKNOWLEDGEMENTS

I would like to express my sincere gratitude to my advisor Dr. Abdessadek

Lachgar for his professional guidance, great patience, enthusiasm, and continuous

encouragement and support, without which this study could not have been accomplished.

I would like to thank my committee members, Dr. Ronald E. Noftle and Dr.

Bradley T. Jones for their helpful advice and support during my entire graduate study. I

would also like to thank Dr. Cynthia S. Day who not only provided tremendous help in

the area of crystallography, but also offered many personal supports.

I am grateful to all faculty and staff members of the Department of Chemistry of

Wake Forest University for creating a positive learning environment. I would also like to

thank Mike Thompson on tremendous help not only in the lab, but also in the personal

life.

I am grateful to all the former and current group members: Postdocs (Dr.

Duraisamy Thirumalai, Dr. Valan C. Amburose, Dr. Bangbo Yan, Dr. Mostafa Taibi, and

Dr. Jianjun Zhang); Graduate students (Ekatherina Anokhina, Huajun Zhou, Zhihua Yan,

Sergio Aaron Gamboa, and Lei Chen); and Undergraduate students (Yumi Okuyama,

Greg Becht, Julien Cosqueric, Barry J. Davis Jr., Mallory Hackbarth and Jenny Nesbitt).

Your help and cooperation will always be in my memory.

I would like to thank those who have collaborated with our group. Dr. Jochen

Glaser (University of Tübingen, Germany) and Dr. Kenneth J. Brown (Winston Salem

State University) helped me during their brief research stay within our group.

V

TABLE OF CONTENTS

Abstract I

Dedication III

Acknowledgements IV

Table of Contents V

List of Tables VIII

List of Figures XI

Chapter

1. Introduction 1

1.1 Materials with Extended Framework 2

1.2 Selected Applications of Open Framework Materials 3

1.3 Metal Phosphate Inorganic Materials 5

1.4 Metal Organic Framework Materials 7

1.5 Metal organo-Phosphate Materials (MOPs) Chemistry 7

1.6 Research Objective 12

1.7 Rationale for Choosing the Building Units 14

1.8 Synthetic Strategies 19

2. Experimental Techniques 23

2.1 Methods of Synthesis 24

2.2 Chemicals Used 26

2.3 Methods of Characterization 28

3. Synthesis, Crystal Structures and Characterization of MOP1 31

3.1 Introduction 32

VI

3.2 General materials and methods 32

3.3 Gallium phosphate oxalates 33

3.3.1 Hydrothermal synthesis 34

3.3.2 Crystal structure determination 36

3.3.3 Results and discussion 41

3.4 Indium phosphate oxalates 50




3.5 Gallium arsenate oxalate 68

3.5.1 Hydrothermal Synthesis 68




4.1 Introduction 77

4.2 Experimental section 78

4.3 Crystal structure determination 81

4.4 Results and discussion 87


5.1 Introduction 97

5.2 General materials and methods 97

5.3 Neutral gallium methyl-phosphonate oxalates 98


VII



5.4 Intercalation of gallium phosphonate oxalates 117

5.4.1 Solvothermal synthesis 118



6. Conclusions 136

References 140

Appendix 157

Scholastic Vita 181

VIII

LIST OF TABLES

Table 2.1 List of Chemicals 26

Table 3.1 Crystallographic Data of MOP1-1 and MOP1-2 37

Table 3.2 Most important bond lengths (Å) and angles (degree) for compound

MOP1-1: [Ga4(PO4)4(H2PO4)(C2O4)]( C4N3H15)(H2O)2.5 39


MOP1-2: [Ga8(H2O)4(PO4)4(HPO4)4(C2O4)4](C10N4H28)(H2O)4 40



MOP1-3: [In6(HPO4)8(C2O4)3]( C10N4H28) 55


MOP1-4: [In4(HPO4)6(C2O4)2]( C10N4H28)(H2O)2 56

Table 3.7 Hydrogen Bond Lengths (Å) and Angles (degree) for Compound MOP1-4

57

Table 3.8 Crystallographic Data of MOP1-5 70


MOP1-5: [Ga6(OH)2(AsO4)2(HAsO4)4(C2O4)3](C10N4H28)·(H2O)3.5 71

Table 4.1 Crystallographic Data of MOP2 compounds 82

Table 4.2 Most important bond lengths (Å) and angles (º) for compound MOP2-1:

Ga(H2O)(PO3CH2PO3)(C6H14N2)0.5 84


84

IX

Table 4.4 Summary of Bond Lengths (Å) and Angles (degree) for Compound

MOP2-2: Ga(PO3CH2PO3H)[(PO3H)2CH2](C2N2H10) 85


85

Table 4.6 Summary of Bond Lengths (Å) and Angles (degree) for Compound

MOP2-3: Ga(C12H8N2)[(PO3H)2CH2](PO3HCH2PO3H2)[(PO3H1.5)2CH2](C12H9N2)

86


93



MOP3-1: [Ga(H2O)(PO3CH3)(C2O4)0.5](H2O) 103


MOP3-2: Ga(H2O)(PO3CH3)(C2O4)0.5 103


and MOP3-2 104

Table 5.5 Layered gallium phosphonate oxalates intercalated by different SDAs

117



Table 5.8 Most important bond lengths (Å) and angles (degree) for 2D compound

MOP3-3, MOP3-4 and MOP3-5: Ga3(PO3CH3)4(C2O4)(SDA)(solvent) 124

X

Table 5.9 Most important bond lengths (Å) and angles (degree) for 1D compound

MOP3-6: Ga(HPO3CH3)(C2O4)2(C10N4H28)0.5(H2O) 126

Table 5.10 Comparison of unit cell parameters of layered gallium phosphonate oxalates

127

XI

LIST OF FIGURES

Figure 1.1 (a) [NH3(CH2)3NH3][Zn6(PO4)4(C2O4)]

(b) In4(4,4’-bipy)3(HPO4)4(H2PO4)4 9

Figure 1.2 Alkylphosphonate and diphosphonate anions 10

Figure 1.3 Zirconium phosphonate layers 11

Figure 1.4 Phosphonate Anions 16

Figure 1.5 Organic Ligands capable of acting as bridging and/or chelating ligands

17

Figure 1.6 Common SDAs or “Templates” 18

Figure 2.1 Two Synthesis Instruments (a) Autoclaves in Furnace (b) Teflon

Pouches and Bag Sealer 26

Figure 3.1 diethylenetriamine (DETA) 1,4-bis(3-aminopropyl) piperazine (APPIP)

33

Figure 3.2 Projection of 3D framework of MOP1-1 along (c) axis showing the

inorganic gallium phosphate tubes bridged by oxalate ligands 41

Figure 3.3 Fragment of the structure of MOP1-1 showing tetramer connectivity

42

Figure 3.4 Environments around Ga(1) and Ga(2) atoms in MOP1-1 43

Figure 3.5 Perspective view along (c) axis of 3D framework of MOP1-2 44

Figure 3.6 Connectivity of gallium phosphate tubes along (a) and (b) axis 45

Figure 3.7 Environments around Ga(1) and Ga(2) atoms in MOP1-2 46

Figure 3.8 TGA of compound MOP1-1 47


XII

Figure 3.10 3D Framework of MOP1-3 showing the inorganic layer on (ab) plane

formed by indium phosphate SBU and linked by oxalate along (c) axis 58

Figure 3.11 Fragment of MOP1-3 showing indium atom environment and connectivity

58

Figure 3.12 3D framework of MOP1-4 showing the channel along (c) axis containing

SDA (H4APPIP)4+ 60

Figure 3.13 Fragment of MOP1-4 showing the tetramers and the connectivity

61

Figure 3.14 Hydrogen bonds in the structure of MOP1-3: Interactions between SDA

and framework; Interactions between water molecules and the framework; Hydrogen

bonds within the framework. 63


Figure 3.16 PXRD comparisons between fresh and dehydrated phase of MOP1-4

66


Figure 3.18 3D framework of MOP1-5 showing the gallium arsenate double layers

bridged by oxalate ligands along (a) axis and (H4APPIP)4+ in the tunnels 73

Figure 3.19 Inorganic double layers formed of two identical gallium arsenates layers

related by an inversion center and bridged through coordinated Ga(2)O4 74

Figure 3.20 Environments of Ga and As atoms showing the atom labeling scheme and

connectivity 74

Figure 4.1 2D framework of MOP2-1 showing the (H2DABCO)2+ between the

gallium diphosphonate layers 87

XIII

Figure 4.2 Projection view of wave-like layer along (c) axis and (a) axis 88

Figure 4.3 (a) Environments of GaO6 (b) Environments of (PO3)CH2 89

Figure 4.4 Hydrogen bonds in the structure of MOP2-1: sandwiched interaction

between SDAs and layer; hydrogen bonds within the layer by coordination water with

InO6 89

Figure 4.5 1D Framework of MOP2-2 showing SDA molecules within the double

chains along (a) axis 90

Figure 4.6 Gallium diphosphonate chain containing symmetry related SBUs and

hydrogen bonds with SDAs 91

Figure 4.7 Environment of gallium atom and diphosphonate units 92

Figure 4.8 (a) Fragment of structure of MOP2-3; (b) Hydrogen bonded layer on (bc)

plane 93

Figure 4.9 TGA of compound MOP 2-1 95

Figure 5.1 3D framework of MOP3-1 consisting of gallium methyl-phosphonate

layers parallel to (bc) Plane 106

Figure 5.2 Fragment of the structure of MOP3-1 showing the atom labeling scheme,

hydrogen bonds and connectivity 107

Figure 5.3 3D framework of MOP3-2 consisting of Gallium methyl-phosphonate zig-

zag layers parallel to (ac) Plane 108

Figure 5.4 Fragment of the structure of MOP3-2 showing the atom labeling scheme

and connectivity 109

Figure 5.5 Solid State NMR spectrum of MOP3-1: Ga(PO3CH3)(C2O4)1/2(H2O)2

110

XIV

Figure 5.6 TGA of Compound MOP3-1 111

Figure 5.7 Comparison of powder X-ray diffraction pattern of MOP3-1 after TGA

Red: fresh MOP3-1; Blue: MOP3-1 after heated at 150°C; Purple: calculated of MOP3-2

112

Figure 5.8 IR spectrum of fresh MOP3-1(blue) and the one after heated at 350°C (red)

113

Figure 5.9 The hydrogen adsorption–desorption isotherms on MOP3-1 at 77 and 87 K

115

Figure 5.10 Powder X-ray diffraction patterns of MOP3-1 before and after H2sorption

study (Red: fresh sample, Blue: after outgassing, Purple: after 77K isotherms + 2hr

outgassing at 60ºC + 87K isotherms) 116

Figure 5.11 2D framework of Ga3(PO3CH3)4(C2O4)(SDA)(solvent) with different

interlayer distances and composition of the layer 128

Figure 5.12 Environments of Ga and P atoms showing the atom labeling scheme and

connectivity 129

Figure 5.13 1D chainlike framework of MOP3-6 130

Figure 5.14 TGA of compound MOP 3-3 131

Figure 5.15 PXRD of compound MOP3-3 (red: before ion exchange, blue: after ion

exchange) 133


exchange) 134


exchange) 135

1

CHAPTER

1 INTRODUCTION

2

1.1 Materials with Extended Frameworks

One of the major areas of materials science is the development of solid state

materials with extended structures that have empty spaces between their components,

such as porous,1 layered,2 or one-dimensional compounds.3 The presence of pores, inter-

layer or inter-chain spaces allows for many applications of these materials. The design of

solid materials (both organic and inorganic) with controlled sizes, shapes and chemical

environments using the principles of crystal engineering has generated enormous interest

in recent years because such designer solids may be exploited for separations, absorption,

ion exchange and catalysis.

Crystal engineering has recently emerged as a major cross-disciplinary field of

basic and applied inquiry. Crystals are comprised of molecules or ions, and the physical

and chemical properties of the crystals depend upon the geometrical arrangement of these

building blocks. From a materials view, control of both the physical and chemical

properties of the materials would be a natural outcome of the ability to predict the crystal

structure of a given compound. The ability to fine-tune features such as color, melting

point, polarity, polymorphism, or conductivity would offer unlimited potential for

materials modification. Unfortunately, it is generally difficult to predict with certainty the

structure of crystalline solids merely from the knowledge of their chemical composition.4

The most successful strategies of crystal engineering are based on the molecular

building block approach, which simplifies the complex problem of structure prediction

into a simple problem of network architecture. For all practical purposes, the crystal

structures are assumed to be networks, where molecules, metals, ions, etc., are considered

as nodes and the intermolecular interactions or coordination bonds represent node

3

connections.5 The design of one, two, or three-dimensional crystalline network structures

can thus be achieved by choosing the desired combination of nodes and connectors.

1.2 Selected Applications of Open Framework Materials

(1) Separation

One of the applications of porous compounds is their use in separation processes.

These materials can function as molecular sieves to separate molecules based on

differences in their size and affinity to the surface of the pores. High selectivity of these

separations arises from well-defined and uniform pore size or interlayer space resulting

from translational periodicity. Porous materials are widely used in industry to purify and

dry gases and solvents. For example, zeolite 4Å is used for drying acetone,6 and zeolite

Li-X is used to separate oxygen from air.7 Besides size and shape-selective separation,

enantio-selective separation can be done by homochiral metal-organic framework

materials. For example, the zinc/D-tartaric acid homochiral open-framework solid can

selectively separate and catalyze trans-esterification reactions.8

(2) Absorption

Microporous inorganic materials such as zeolites can be used as absorbents of

natural gas.9 With more flexible rational design metal-organic frameworks (MOFs) are

widely regarded as promising materials for gas storage. For example, the zinc 1,4-

benzenedicarboxylate series of MOFs can be used to absorb methane after removing the

guest molecules.10,11

4

(3) Ion Exchange

Some open-framework compounds have accessible cationic sites which allow for

ion exchange. This is used, for example, in nuclear waste treatment to remove radioactive

isotopes12 and in detergents to soften water by removing magnesium and calcium ions.13

(4) Catalysis

(a) Heterogeneous catalysis

The high surface area of some extended framework materials and the possibility

to introduce active sites to this surface has led to extensive applications of porous and

layered compounds in heterogeneous catalysis.14 For example, acidic clay catalysts are

used in the synthesis of gasoline anti-knock additives, such as methyl t-butyl ether.15

Zeolite ZSM-5 is used to convert methanol to olefins.16 Manganese porphyrin complexes

can be immobilized on zinc phosphonates by attachment to the phosphonate group

leading to the formation of a hybrid zinc phosphonate framework that has similar

catalytic efficiency for the epoxidation of cyclooctene, thus combining the advantages of

homogeneous and heterogeneous catalysts. 17 Sn-zeolite beta can be used as

heterogeneous chemoselective catalyst for Beayer-Villiger oxidation, in which a ketone is

oxidized to an ester. 18 The advantages of using these materials over homogeneous

catalysts are milder synthesis conditions, convenient separation from the reaction mixture

by filtration and easy recovery of the supported ligands.

(b) Shape-selective catalysis

The size discrimination is also a basis for the use of porous compounds in

heterogeneous catalysis. 19 They can stop unwanted components from entering the

5

reaction which is used in the process of catalytic dewaxing of gasoline, i.e. converting

paraffins with poor octane numbers into gaseous products or branched isomers;20 or to

prevent the escape of byproducts from the pores which is used, for example, in the

synthesis of p-xylene (a precursor in the production of polyester fibers).21 These materials

can also be used to suppress a competing reaction going through a transition state or an

intermediate which does not fit the size of the pores.22

(c) Redox catalysis

Conventional porous compounds and clays are based on aluminosilicate23,24 or

aluminophosphate 25 frameworks, which are not useful in reactions involving redox

processes. Recent research in this field focuses on including redox centers, such as

transition metals and phosphonates as components of the frameworks, which extend their

applications to selective redox catalysis.26 For example, the titanium analogue of zeolite

ZSM-5 can selectively catalyze epoxidation of olefins.27 In addition, porous or low-

dimensional materials containing redox centers can be used for intercalation of not only

neutral species but also cations. This is the basis of the applications of these materials as

electrodes in solid-state batteries.28 For example, layered transition metal dichalcogenides,

such as TiS2, have been shown to have good performance as cathodes in lithium

batteries.29

1.3 Metal Phosphate Inorganic Materials

The research of inorganic-framework materials represented by silicates (zeolites)

and metal phosphates has led to important findings in fundamental and applied materials

6

science.30 These two classes of materials have similar topologies and consist of inorganic

tetrahedral molecular building blocks (SiO4)4- or (PO4)3- and (AlO4)5-.

Aluminum phosphates were first discovered by Flanigen and co-workers in

1982,28 and a large number of aluminum-based phosphate materials is now known. The

inorganic framework is constructed around organic templates (structure directing agents)

the same as zeolite. The zeolites’ frameworks are generally stable after the templates are

removed. In most metal phosphate cases, there is a clear relationship between the

framework architecture and the shape, size and charge of the template molecule.31 Only

few metal phosphate frameworks are porous after calcination and exhibit reversible

adsorption and desorption behavior.32,33

In the mid-1980s, research was extended to gallium as a complete replacement for

aluminum and produced a series of gallophosphates related to the AlPO4-n family.34 The

aluminum and gallium can have four-, five- or six-fold coordination. Indium, however,

only shows octahedral coordination which is confirmed by all the reports of organically

templated indium phosphates.35 Other main group metals such as beryllium36 and tin37

phosphates have been prepared. Following the successful introduction of transition

metals into the zeolitic aluminum phosphates, many transition metal phosphates which

may contain metals in different valence states and different coordination numbers have

been synthesized, such as cobalt, 38 iron, 39 manganese, 40 molybdenum, 41 nickel, 42

titanium,43 vanadium,44 zinc45 and zirconium46. The structural diversity of these systems

has increased in the sense that, whereas the zeolites and early aluminophosphates were

based entirely upon corner-sharing tetrahedra ([SiO4], [AlO4] etc.), many of the newer

architectures involve other polyhedra such as octahedra [XO6], pentacoordinated [XO5],

7

square pyramidal [XO4] or [XO3] units. These exciting developments are gradually

having an impact on the applications of such materials. Although the traditional

applications of open-framework materials continue to be dominated by the

aluminosilicate zeolites, which are noted for their stability and find utility in catalysis,

separations, and ion-exchange, the new generation of materials offers a wider range of

chemical and physical properties that are beginning to be explored.

1.4 Metal Organic Framework Materials

A breakthrough in the world of porous materials was achieved in the late 90s’

mainly from coordination and organometallic chemistry. Porous metal-organic

frameworks were prepared using supramolecular assemblies composed of metal centers

or polynuclear clusters and multi-topic organic ligands as linkers.47

Carboxylate, amine, and pyridine derivatives or molecules with combined

functionalities are mainly used as linkers. Rigid linkers, such as 1,4-benzene

dicarboxylate (terephthalate), have been used to design an extensive variety of

coordination polymers,48 while flexible linkers, such as succinate and glutarate, have led

to the creation of a wide range of less predictable structures.48

1.5 Metal organo-Phosphate Materials (MOPs) Chemistry

Metal organo-phosphate materials (MOPs) can be considered as intermediates

between zeolite-like materials in which all components are inorganic, and metal-organic

framework materials which are based on inorganic nodes linked via organic linkers.

Organo-phosphate frameworks consist of inorganic nodes connected via inorganic and

8

organic linkers. Three types of metal organo-phosphate materials (MOPs) can be

engineered and prepared:

(1) Metal Phosphates linked by Multi-dentate Organic Ligands

In this class of MOPs multi-topic organic ligands are used to link inorganic metal

phosphate clusters, chains, or layers to form hybrid frameworks.

Organic ligands can be combined with metal phosphates to prepare materials built

of both inorganic (stable and rigid) and organic (flexible and tunable) structural

motifs.49,50 The oxalate ligand (C2O4)2- represents the simplest ligand that can act as a

linker between inorganic species. Accordingly, a number of metal oxalate framework

have been reported in recent years.51 A few metal phosphate-oxalates built of inorganic

metal phosphate chains or layers linked via oxalate units have been characterized

recently.52,53,54,55,56,57,58 Figure 1.1 (a) shows an example of a 3D framework composed of

zinc phosphate inorganic layers connected via the oxalate linker.59 The work has also

been expanded to other ligands such as polynitriles, pyridine derivatives, and amino

acids.60,61 In Figure 1.1 (b) 4,4’-bipyridine ligands act as linkers between neutral indium

phosphate sheets.62

9

Figure 1.1 (a) [NH3(CH2)3NH3][Zn6(PO4)4(C2O4)] (b) In4(4,4’-bipy)3(HPO4)4(H2PO4)4

Oxalate: (C2O4)2- 4,4’-bipy: 4,4’-Bipyridine

(2) Metal Phosphonates

The use of phosphonates as building blocks is an attractive strategy since it allows

for integrating the organic parts into phosphates prior to the preparation of the final

material, which allows for functionalization of the building blocks.

The field of metal phosphonate materials containing O3PR groups, where R is an

organic functional group, is expanding at a rapid pace because these materials display

varied and potentially important properties. The research started with the discovery of

layered zirconium phosphonates reported in 1978.63 Structural similarity between metal

phosphonates and corresponding phosphates was also revealed through research on

layered phosphonates and tailored design of these materials became possible.64

Phosphonate anions (Figure 1.2) function as linkers connecting inorganic oxide

frameworks and organic functional groups. Tailored design of the linker molecules is

Oxalate Linkers 4,4’-bipy Linkers

10

easy because phosphonic acids are prepared in relatively simple procedures. The choice

of the organic group R can greatly affect the properties of the resulting materials.

Figure 1.2 Alkylphosphonate and diphosphonate anions

Unlike organically modified mesoporous silicas in which the Si–C bond of the

methylene-bridged organosilane used as the silicon source can be cleaved under strongly

basic hydrothermal conditions, chemical and thermal stabilities of organophosphonic

acids and moderately mild hydro- or solvo-thermal synthetic conditions for metal

phosphonates led to exploring this system. The chemical and thermal stability of

phosphorus–carbon bonds in phosphonates allows the preparation of robust inorganic–

organic hybrid materials.

Most metal phosphonates have a structure that can be described as formed of

inorganic layers, consisting of metal ions coordinated by PO3 groups, with the organic

functional group pendant in the interlayer region. In rare cases cross-linking results in the

formation of porous materials. In these materials, divalent transition metals such as Zn,

Cu, Co, Ni, and Mn are successfully used as metal sources, but trivalent Al, Ga, In and

tetra- or pentavalent V are also important.

The number of organophosphonic and organodiphosphonic acids that have been

investigated is not large. Simple phosphonates,65 where R is an alkyl chain or phenyl

group, have been investigated, whereas recent studies have involved more complex

4-

P PO

O O

O

OO

( )nPO

O

O

R

2-

11

groups, such as crown ethers, viologens and bipyridyls.66 Other organophosphonic acids

used to date include carboxylate functional groups67 (known as phosphonocarboxylates),

which are ideally suited for structural cross-linking of metal phosphonate materials.

For example, the structure of zirconium phosphonates can be described as

consisting of inorganic Zr(PO3)2 layers with R groups pointing between the layers (Figure

1.3). If diphosphonates are used, then the layers can be cross-linked to form 3D

frameworks.

Figure 1.3 Zirconium phosphonate layers

(3) Metal Phosphonates linked by Organic Ligands

The design and synthesis of these materials combine the two approaches mentioned

above. In this case, organic ligands are used to link or coordinate the metal phosphonate

building blocks to form hybrid frameworks.

Only a few reports in the literature illustrate the use of organic ligands as part of the

structure along with the phosphonate groups. The first examples, Sn2(O3PCH3)(C2O4) and

Sn4(O3PCH2CH2CO2)2(C2O4) are metal oxalatophosphonates, 68 that consist of two

ZrP2O6 layer

R R R R R R

R R R R R R

ZrP2O6 layer

R R R R R R

R R R R R R

12

different organic parts, one directly attached to the phosphate group and the other (C2O4)

acting as linker. Recently lanthanide oxalate-aminophosphonate hybrids with a 3D

framework have been synthesized and characterized.69 Also metal oxalate-phosphonates,

such as (C3H12N2)0.5[Ga3(C2O4)(CH3PO3)4]⋅0.5H2O with a layered structure, and 3D

Na2Fe/Mn3(C2O4)3(CH3PO3H)2 analogues have been reported by K-H Lii’s group.70

Organic ligands, with nitrogen-based donor sites, such as pyridine derivatives and

phenanthrolines were also used to link transition metal phosphonate layers or chains to

form novel hybrid frameworks, for example, Cu4[CH3C(OH)(PO3)2]2(pz)(H2O)4,

CuI2CuII[CH3C(OH)(HPO3)2]2(4,4’-bipy)2(H2O)2, Zn(PO3R)(2,2’-bipy) and

Zn(PO3R)(phen). (R= CH3, C2H5, C6H5, C6H5CH2) 71

1.6 Research Objective

The objective of the research conducted within the framework of this thesis is to

prepare novel hybrid metal phosphates and phosphonates that incorporate organic species

as part of their framework. The primary motivation for the study is to investigate the

chemistry and reactivity between different species involved and to study their crystal

structures. The results from this investigation will lead to a better understanding of the

structure-determining factors, which may allow the preparation of future useful materials.

The phosphates of group 13 metals such as aluminium, gallium and indium are of

particular interest since they show a wide structural diversity. Many have framework

topologies analogous to zeolites, while others have unique structures. So our research

mostly focuses on group 13 metal organo-phosphate materials, which start with gallium

13

phosphate oxalate hybrid open framework materials, and is expanded to the use of indium

as the metal center.

Our research goal is to prepare and characterize novel organic-inorganic hybrid

metal organo-phosphate materials (MOPs). The MOPs we discovered can be classified

into three different types of hybrid frameworks:

MOP1: Hybrid frameworks built of inorganic metal phosphate (MPO4) layers or

chains linked or coordinated via organic functional ligands such as oxalate, 1,10 –

phenanthroline, 4,4’-bipyridine and other chelating or bridging ligands.

MOP2: Hybrid frameworks built of metal phosphonates (MPO3R) or metal

diphosphonates (MPO3RPO3) in which the phosphonate anions can be modified by

changing the organic functional groups (R) covalently bonded to -PO3.

MOP3: Hybrid frameworks built of metal phosphonate (MPO3R) layers or chains

linked or coordinated via organic functional ligands. These frameworks can be

considered to be a combination of the previous two types.

These materials are organic-inorganic hybrid materials that have become of much

interest as a molecularly engineered open framework structure in recent years. Ideally

they contain the inorganic metal phosphate and oxide phases with the incorporation of

organic substructures which are not only used as structure-directing and charge-

compensating agents generally located inside the pores or in the interlayer spacing of the

open-framework, but also act as ligands or linkers that are either part of the inorganic

framework or link different inorganic modules, i.e. chains or layers to form either 2D or

3D frameworks.

14

1.7 Rationale for Choosing the Building Units

In this work we conducted a systematic study of the preparation and

characterization of metal organo-phosphate materials (MOPs), focusing on the use of

different building blocks as well as the effect of the synthetic conditions.

(1) The Metal

The most important component of metal organo-phosphates is the metal center

which coordinates with phosphate or phosphonate through oxygen atoms. The research

here focused on group 13 metals in which gallium is the main choice.

Only a few lower group 13 metal (Ga, In) organo-phosphates have so far been

reported. Most of our work will concentrate on the synthesis and characterization of

gallium and indium MOPs and some transition metals MOPs for comparison such as zinc

and manganese. The donor atoms in the coordination ligands can be varied from oxygen

to nitrogen and sulfur. Unlike aluminosilicates which have frameworks based on

tetrahedra, gallium and transition metals can adopt 4- (tetrahedral), 5- (trigonal

bipyramidal) and 6- (octahedral) coordination in oxygen or nitrogen-based polyhedra,

and indium shows only six-coordination in all known indium phosphate and

phosphonates.

(2) The Tetrahedral Building Unit

The tetrahedra group (PO4) coordinates with metal cations through oxygen

bridges to build thermal stable inorganic frameworks. To extend the research from this

point of building block, the phosphonate anion (POnR4-n) represents a more important and

interesting part to form relatively thermal stable inorganic framework. And it can be

15

chemically modified or functionalized by the connecting organic R group to produce or

tune the physical and chemical properties of the solid materials.

The organophosphonic acids are the most useful and versatile source of the

building units of hybrid inorganic-organic materials because of their structural diversity

and the relatively simple synthetic procedure required. The chemical and thermal stability

of phosphorus-carbon bonds in phosphonates is high enough that decomposition under

the synthetic conditions of the solid materials does not take place.

The research strategy is to use different ligands to form frameworks with different

topologies. Attaching different organic functional groups on the phosphonate ligands

through oxygen or nitrogen donor atoms may lead to modification of the structure and

thus the properties of the MOPs being produced. While initial work in phosphonate

systems focused on simple alkyl- and arylphosphonates, multifunctional ligands have

been used to produce materials with a wide range of dimensionalities and structures.

Several strategies can be adopted for functionalizing phosphonates, including adding a

second, unique functional group such as an amine, hydroxyl, carboxylic acid or crown

ether; incorporating a second phosphonate into a single ligand to produce

bisphosphonates; or integrating two or more additional functional groups into the

phosphonate ligand. The additional functional groups can either serve to coordinate to the

metal center or provide a potential reactive site that can be used for a process such as

catalysis or adsorption; it is possible to make multifunctional ligands to do both. Figure

1.4 shows the molecular formulas of some phosphonate anions with different organic

functional groups that can be used in synthesis.

16

P OO

O

O 3-

P CH3O

O

O

2-

PO

O

O

2-

P CH2O

O

O

P O

O

O

4 -

P CH2

O

O

O

C

O

O

3-

P C

O

O

O

P

5-CH3

O

O

O

O

Figure 1.4 Phosphonate Anions

Since phosphorus and arsenic belong to the same group in the periodic table and little

work has been carried out on the arsenate as compared to the phosphates, we can use the

arsenate group as a building unit and study some metal organo-arsenates (MOSs) which

may be iso-structural with the corresponding MOPs.

(3) The Organic Linker

The idea is to use specific organic ligands that can link or modify the inorganic

network during the reaction to make materials with specific hybrid architecture. The

flexibility of the organic parts allows us to tailor the functionality within a wide range.

In order to act as a linker, the ligand has to have at least two coordination

positions which allow it to link the building blocks. The multidentate organic ligands

(which can coordinate with metal cations through oxygen or nitrogen, such as

polycarboxylic acids, polynitriles, pyridine derivatives, and amino acids) are chosen as

the most flexible building units in the hybrid inorganic-organic structures. The simplest

carboxylic acid to be used is the rigid oxalate anion which has four potential oxygen

donor sites to bridge the metal phosphate layers or chains and leads to many successes in

17

the synthesis of hybrid materials. Figure 1.5 shows the molecular formulas of some

organic ligands that can be used as linkers.

The advantages of using organic linkers are: first, the large variety of readily

available organic groups that can serve as linkers; second, the ability to be functionalized

gives a choice of organic ligands to produce desirable physical and chemical properties

such as adsorption and catalysis.

The disadvantage is the difficulty of synthesis with both the organic ligands and

inorganic phosphate or phosphonate anions coordinating to the metal centers at same time

due to differences in solubility, pH stability of different deprotonated components, and

thermal stability.

C C

OHOH

O O

O

OH OH

O

N C

R

HH

O

OH

H

Oxalic Acid Terephthalic Acid Amino Acid

O

Cl

OH

O

Cl

OH

N N

N N

Chloranilic Acid 4,4’-Bipyridine 1,10-Phenanthroline

Figure 1.5 Organic Ligands capable of acting as bridging and/or chelating ligands

18

(4) The Structure Directing Agent (SDA)

Metal phosphates or phosphonates are commonly synthesized with use of organic

amines as structure directing agents (SDA). A large number of amines (primary,

secondary, tertiary, or quarternary; linear, branched, or cyclic) are used to organize the

inorganic or hybrid organic-inorganic materials into different types of frameworks. Using

SDAs with different size, shape or chemical nature (e.g. pKbs) leads to the rational design

of the framework topologies such as dimensionalities and tailored connectivities.72 Figure

1.6 shows some SDAs commonly used in solvo-thermal synthesis.

H2N

HN

NH2 Diethylenetriamine (DETA)

H2NNH2

NHHN NN

N N

H2N

NH2

Ethylenediamine

(en)

Piperazine

(PIP) DABCO

1,4-bis(3-aminopropyl) piperazine

(APPIP)

Figure 1.6 Common SDAs or “Templates”

Based on their role and their effect during the synthesis, SDAs can be divided into

at least two classes. First, “templating” occurs when the open-framework structures adopt

the geometric and electronic configurations that are unique to the templating molecule. In

this case, the framework of the extended material retains the shape of that molecule upon

removal of the organic templates.73 Second, SDAs can act as space fillers, which can

19

increase the thermodynamic stability of the composite, simply due to van der Waals’

interactions, π-π stacking or hydrogen bonds between the SDAs and the framework.

(5) Solvent

Solvent molecules are also important building units of the structure. They can act

as filling components in the voids generated by the framework, i. e., interlayer spacing,

channels, or cavities. Sometimes they act as ligands coordinated to the metal ions to

block active coordination sites. This is a desirable structural aspect of extended materials

as the solvent-metal coordination bond is generally weak, and the solvent ligand is quite

labile, which provides metal sites that can be catalytically active. Since here most

reactions are carried out under hydrothermal conditions, water is the most common

solvent since it is a good solvent for most metal salts, organophosphonic acids, organic

ligands such as carboxylates and SDAs. To improve the crystallization other solvents-

mainly alcohols (methanol, ethanol, ethylene glycol), THF and DMF will also be

explored.

1.8 Synthetic Strategies

In order to facilitate the formation of MOPs and determine their structures, the

main synthetic method employed is hydro- or solvo-thermal reactions at 80-200˚C, which

has led to the synthesis of a number of products that cannot form by direct precipitation.

The reason for choosing this synthetic method is based on findings in the synthesis of

zeolites and molecular sieves.78 Thus, it is well known that inorganic polymers and

hybrid inorganic-organic frameworks with extended structures cannot easily form under

20

ambient conditions. On the other hand, it is not possible to use high-temperature solid

state synthesis since most organic species decompose at high temperature. Moreover and

probably more important is that mild solvo-thermal conditions have been shown to be

suitable for crystal growth allowing for formation of crystals suitable for crystal structure

analysis using single crystal X-ray diffraction.

Another synthetic approach is the reaction of molten phosphonic acids with

inorganic salts of the required metal. This method has been shown to be particularly

successful in the synthesis of nickel,74 copper75 and aluminum phosphonates.76,77 The

limitation of this method is that the phosphonic acid must melt rather than decompose at

elevated temperatures.

From the same metal and phosphonate, variations of synthetic parameters such as

phosphonate source, metal source, metal/P ratio, solvent, absolute and relative

concentrations of reactant, the pH of the reaction mixture, and reaction temperature can

lead to a number of different phases with different structural and chemical properties

under hydro- or solvo-thermal conditions.

(1) In this dissertation the source of the metal starting materials from metal

oxides to metal nitrates and acetates was varied. This affects the solubility and, thereafter,

concentration of the metal ions in solution, which can lead to the stabilization of different

compounds.

(2) Reaction temperatures can affect the autogenous pressure and crystal

growth. Different types of MOPs need different optimum temperature and different

solvent.

21

(3) The pH value of the starting solution is important since it dictates the

stability of different species and affects the solubility of the starting materials. Adjusting

the pH value of the solution before the reaction can change the initial composition and

thus affect the composition and stability of the products. The pH is adjusted by

controlling the amount of acid (such as HCl, HF, H2SO4) added in the starting solution.

(4) Since the nature of the interaction between the solvent and the reacting

species is critical to the outcome of solvo-thermal synthesis, organic solvents can be used

with or without water. They can be grouped into four categories based on their tendency

to form hydrogen bonds: high, high-medium, low-medium and non-hydrogen-bonding.

Many non-aqueous solvents are already used in the synthesis of molecular sieves such as

alcohol, ethylene glycol, glycerol, pyridine, DMF, DMSO, and all kinds of amines.78 The

combination with water or two immiscible solvents is a common technique for

crystallizing compounds at low to moderate temperatures.79 Also the biphasic synthesis

offers advantages over conventional hydro- and solvo-thermal methods on hybrid

materials synthesis because the organic building blocks usually have a different solubility

from the inorganic ones.80

(5) As described above, the SDAs are generally located in the channels and

cavities of the framework and, in some cases, can be removed by post-synthesis treatment

such as calcinations or chemical extraction.32,33 Another function of the SDAs is to

intercalate between the inorganic or hybrid layers and support the structure through

hydrogen bonds. Sometimes the SDAs can play dual roles, acting as the templates and as

coordinating or chelating ligands and are thus included in the framework.81

Different protonated organic amines as SDAs were used.

22

(a) Vary the shape, size and charge of protonated organic amines as SDAs to

get frameworks with different charges topologies and geometries.

(b) Vary the synthetic conditions to make the solvent molecules themselves

act as SDAs producing materials with neutral frameworks which are rare and important

in application and novel structural features. The advantage is that the neutral solvent

SDAs can be easily removed without breaking the framework.

Many studies have now shown that a large family of metal ions can react with

phosphoric acid (H3PO4), phosphonic acid (H2PO3R), diphosphonic acid (H2PO3RPO3H2)

and organic ligands to yield different dimensional compounds. However, only a few

lower group ΧΙΙI metal (Ga, In) organo-phosphate have so far been reported. Most of our

work is concentrated on the synthesis and characterization of gallium and indium MOPs.

23

CHAPTER

2 EXPERIMENTAL TECHNIQUES

24

2.1 Methods of Synthesis

Hydro- and Solvo-thermal synthesis

The synthesis of zeolites, metal phosphates or phosphonates, and hybrid inorganic

organic materials is generally carried out hydrothermally under autogenous pressure.

Hydrothermal synthesis refers to reactions in aqueous media above 100 ºC and 1 atm.

These conditions generally favor the dissolution of reactants that are difficult to dissolve.

This method is not limited to open-framework materials but can be used to synthesize a

wide range of crystalline materials including quartz, complex oxides, fluorides, and

hybrid materials. Rabenau and Laudise have published an excellent and extensive review

of the hydrothermal synthesis method describing its role in preparative materials

chemistry and crystal growth.82 One of the most important advantages of hydrothermal

synthesis over conventional synthetic methods is that it favors formation of low

temperature phases and metastable compounds. Feng and Xu have described a large

number of new materials that have been synthesized under hydrothermal conditions.83

Two major differences exist between the chemical conditions of hydrothermal

synthesis of zeolites and metal phosphates: 1) The synthesis of zeolites is carried out in

basic medium, while metal phosphates are obtained under highly acidic conditions; 2) In

zeolites, both inorganic cations and organic amines or ammonium ions are used, while for

phosphates, mostly organic cations are used. In a typical hydrothermal synthesis of metal

phosphates, for example, a metal salt or metal oxide is dissolved or dispersed in water

with stirring, and the phosphate source (H3PO4) is added to the solution resulting in a

highly acidic reaction mixture. Either an amine or ammonium salt is added, which

slightly reduces the acidity of the solution. The reaction mixture is transferred to a Teflon

25

beaker with approximate fill factor ∼40-50%, sealed in a stainless steel autoclave, and

heated to 125-250 ºC for 18-72 h. At the end of the reaction, the autoclave is removed

from the oven, cooled to room temperature, and opened. The solid product obtained is

filtered and washed thoroughly with water. The products are initially characterized by the

use of a powder X-ray diffraction (PXRD) pattern that helps determine if the product is a

mixture or a pure phase, and if it corresponds to a known or an unknown phase. The

presence of organic species, amines, ammonium ions, or organic linkers and functional

groups on the phosphonate groups is determined by IR spectroscopy. Energy-dispersive

X-ray analysis (EDAX) gives the metal/phosphorus ratio, while gravimetric analysis

gives the total amount of solvent and amine. If the material is a new phase, its structure

can be solved by single-crystal X-ray diffraction method.

The synthesis of metal organo-phosphate materials (MOPs) is generally carried

out in Teflon-lined autoclaves (Parr) or sealed heavy-wall glass tubes with PTFE caps

(Ace Glass) at temperatures between 120 and 250 ˚C. The crystals grow under high vapor

pressure of different solvents. The reaction-crystallization is a multiphase process,

commonly involving at least one liquid phase and both amorphous and crystalline solid

phases.84

The general reaction equation can be written as:

Metal source + Phosphate source + Organic linker + Amine + Solvents

In a typical solvo-thermal reaction, 1 mmol metal oxide or nitrate is mixed with

different ratios of phosphonic acids and organic linkers in 6-7 ml buffer and solvents,

120–180 °C 18–72 h

26

then sealed and heated in 23 ml capacity Teflon-lined autoclaves or heavy-wall glass

tubes under different temperatures. For smaller amounts of product, metal salts can be

mixed with phosphonic acid and organic linker in 1ml buffer and solvents, then sealed in

a 2×2 inch transparent Teflon pouch prepared using a table top bag sealer (Aline Heat

Seal). Six to eight pouches can be placed into a 125 ml capacity Teflon-lined autoclave

and backfilled with 35-40 ml solvent before heating.

Figure 2.1 Two Synthesis Instruments

(a) Autoclaves in Furnace (b) Teflon Pouches and Bag Sealer

2.2 Chemicals Used

Table 2.1 contains all chemicals used in the dissertation with their origin and purity

Table 2.1 List of Chemicals

Chemical Purity Origin

Ga2O3 99.99% Atlantic Metals and Alloys

In2O3 99.9% Alfa Aesar

In(NO3)3(H2O)3 99.9% Sigma-Aldrich

27

Mn2O3 98% Alfa Aesar

Zn(CH3COO)(H2O)2 99.9% Fisher

HCl 12.1M Fisher

HNO3 15.8M Fisher

H3BO3 99.9% J.T. Baker Chemical Co.

H3PO4 85% Fisher

As2O5(H2O)3 99% Sigma-Aldrich

H2C2O4(H2O)2 100.4% Fisher

H2PO3CH3 98% Sigma-Aldrich

H2PO3C6H5 98% Sigma-Aldrich

H2PO3CH2PO3H2 99% Sigma-Aldrich

H2PO3CH2COOH 98% Sigma-Aldrich

diethylenetriamine (DETA) 97% Alfa Aesar

ethylenediamine (en) 99% Sigma-Aldrich

piperazine (PIP) 99% Sigma-Aldrich

1,4-diazabicyclo [2.2.2] octane

(DABCO) 98% Sigma-Aldrich

1,4-bis(3-aminopropyl) piperazine

(APPIP) 97% Sigma-Aldrich

1,10-phenanthroline (1,10-phen) 99% Sigma-Aldrich

CH3CH2OH (EtOH) 200 proof McCormick

HOCH2CH2OH (eg) 99+% Fisher

Tetrahydrofuran (THF) 99+% Fisher

28

2.3 Methods of Characterization

(1) Elemental analysis

Elemental composition of the reaction products such as metals and phosphorus is

determined by Energy-Dispersive X-ray Analysis (EDAX), while C, H, N analyses were

performed by combustion using automatic analyzers.

(2) Powder and single-crystal X-ray diffraction

The reaction products were initially characterized by the X-ray powder diffraction

(XRPD) technique at room temperature using a BRUKER P4 general-purpose four-circle

X-ray diffractometer modified with a GADDS/Hi-Star detector positioned 20cm from the

sample. This method allows a convenient identification of known phases, as well as

determining whether a compound belongs to a known structural type. The crystal

structures of the new compounds were determined by single crystal X-ray diffraction

techniques using a Bruker Smart Apex diffractometer equipped with a CCD area

detector system, a graphite monochromator and a Mo Kα fine-focus sealed tube (λ =

0.71073 Å) operated at 1.5KW power (50 kV, 30mA). Initial positional parameters for

indium, phosphorus, and oxygen atoms were determined using direct methods, and the

structure was refined using full-matrix least-squares techniques (Bruker AXS

SHELXTL).85

(3) TGA analyses

The thermal stability of the new materials was studied using a Perkin-Elmer Pyris

thermogravimetric analyzer in air or an inert atmosphere such as nitrogen or argon. The

29

phase of each decomposition step was characterized by X-ray powder diffraction and

infrared spectroscopy.

(4) IR spectroscopy and Solid-State NMR

Infrared vibrational spectroscopy is a useful tool for the characterization of metal

organo-phosphates, since it can provide information about the existence and the

coordination mode of organic moieties, such as -COOH and -C6H5, and incorporation of

organic amine templates and water molecules.

Solid state NMR is an efficient tool that provides accurate insights into the local

environments of Ga, P and H present in these hybrid (organic/inorganic) MOPs and can

selectively examine the inorganic part, the organic part, and their connection. 1H and 31P

NMR solid state spectra can provide the chemical environment of the PO3 group. Gallium

has two NMR active isotopes, 69Ga and 71Ga, both having I = 3/2 spins with larger

gyromagnetic ratio and lower quadrupole moment for 71Ga, which is thus the easier to

observe.86 71Ga solid state spectra can provide the correlation that links the gallium

chemical shifts for four- and six- fold coordination in silicate, phosphate and organic

complexes.

(5) Properties studies

One of our motivations for the preparation of low-dimensional and open-

framework cluster materials is their potential use ion exchange materials and adsorption.

a) Ion exchange studies were carried out heterogeneously and the phases obtained

were characterized by phase technique X-ray powder diffraction. One way is using

30

smaller cations to replace the cations in the porous materials to get more inner surface

area and free volume. The other way is using bigger cations to replace the cations in

layered or 1D polymeric materials to get larger inter-layer or inter-chain distance.

b) Adsorption studies were carried out on the automated micropore gas analyzer

Autosorb-1 MP (Quantachrome Instruments). The information obtained such as surface

area, pore size distribution and gas adsorption abilities for H2 and inert gas like N2 are the

basis of their applications such as absorbents or catalysts.

31

CHAPTER

3 SYNTHESIS, CRYSTAL STRUCTURES AND CHARACTERIZATION OF

MOP1

32

3.1 Introduction

This chapter describes the synthesis, structural and chemical characterization of

MOP1 type hybrid frameworks compounds prepared in the course of this dissertation.

These compounds are the first type of metal organo-phosphate hybrid materials (MOPs),

which are built of pure inorganic metal phosphates (MPO4) layers or chains linked or

coordinated by organic functional ligands such as oxalate (C2O4)2-.

Here we have synthesized and studied two gallium phosphate oxalates (MOP1-1,

MOP1-2), two indium phosphate oxalates (MOP1-3, MOP1-4) and one gallium arsenate

oxalate (MOP1-5).

3.2 General materials and methods

Chemicals used were of reagent quality and were obtained from commercial

sources without further purification as shown in Table 2.1 in Chapter 2.

X-ray powder diffraction data were collected at room temperature using a

BRUKER P4 general-purpose four-circle X-ray diffractometer modified with a

GADDS/Hi-Star detector positioned 20 cm from the sample. The goniometer was

controlled using the GADDS software suite. The sample was mounted on tape and data

were recorded in transmission mode. The system employed a graphite monochromator

and a Cu Kα (λ = 1.54184Å) fine-focus sealed tube operated at 1.2 kW power (40kV,

30mA). Thermogravimetric analysis (TGA) was carried out between 30 and 800 °C

under a flow of air or N2 with a heating rate of 10 °C/min using a Perkin-Elmer Pyris

thermal analyzer. FTIR spectra were recorded on a Galaxy Series FT-IR 4020 (Madison

Instruments Inc.) in the range from 400-4000cm-1 using the KBr pellet method.

33

3.3 Gallium phosphate oxalates

MOP1-1: [Ga4(PO4)4(H2PO4)(C2O4)](H3DETA)(H2O)2.5 has a 3D framework

that is made up of inorganic gallium phosphate tubes filled with protonated

diethylenetriamine (DETA) along the (c) axis and cross-linked via organic oxalate

ligands. The hybrid framework generates 9×9 Å2 channels along the (c) axis containing

water molecules. When larger and higher charged SDA such as 1,4-bis(3-aminopropyl)

piperazine (APPIP) was used, the synthesis led to a series of novel metal

phosphate/arsenate oxalates.

MOP1-2: [Ga8(H2O)4(PO4)4(HPO4)4(C2O4)4](H4APPIP)(H2O)4 also has a 3D

framework that is made up of inorganic gallium phosphate tubes along the (c) axis cross-

linked via organic oxalate ligands in (a) and (b) directions. The hybrid framework also

generates 9×9 Å2 channels containing protonated 1,4-bis(3-aminopropyl) piperazine

(APPIP) along the (c) axis.

Figure 3.1 shows chemical structure of the two SDAs.

H2N

HN

NH2

N N

H2N

NH2

Figure 3.1 diethylenetriamine (DETA) 1,4-bis(3-aminopropyl) piperazine (APPIP)

34

3.3.1 Hydrothermal synthesis

MOP1-1: [Ga4(PO4)4(H2PO4)(C2O4)](H3DETA)(H2O)2.5 was prepared starting

from a mixture containing Ga2O3, HCl (3M), H3PO4, H2C2O4·2H2O, DETA, DABCO,

and H2O at a molar ratio of 1:6:4:2:2:2:400.

Ga2O3 + 6 HCl + 4 H3PO4 + 2 H2C2O4(H2O)2 + 2 DETA + 2 DABCO + 400 H2O

MOP1-1 : [Ga4(PO4)4(H2PO4)(C2O4)](H3DETA)(H2O)2.5

In a typical synthesis, 0.158 g of Ga2O3 (0.84mmol) was dispersed in 4.3 mL of

water and 1.7 mL of HCl (3M) with stirring; 0.23 mL of H3PO4 (3.36mmol, aqueous 85

wt %), 0.2125 g of H2C2O4(H2O)2 (1.68mmol), and 0.19 mL of DETA (1.68mmol) were

added with continuous stirring and the mixture was homogenized for ~30 min. 0.192g of

1,4-diazabicyclo [2.2.2] octane (DABCO) (1.68mmol) was added to adjust the pH of the

starting mixture to 2.94. Then the starting mixture (~7 mL) was transferred to a 23-mL

capacity PTFE-lined stainless steel autoclave (Parr, Moline, IL), sealed and heated at 150

°C for 72 hours under autogenous pressure followed by slow cooling to room temperature

at 10 °C/h. The pH of the mixture after reaction was measured and found to be 3.83. The

resulting product which consisted of colorless plate-shaped crystals of MOP1-1 obtained

in 72% yield based on gallium was filtered and washed with deionized water and acetone

and dried in air. Elemental analysis confirmed the number of tri-protonated DETA,

oxalates, and water molecules per formula unit. Calcd: C, 7.25%; N, 4.23%; H, 2.23%.

Found: C, 7.14%; N, 4.10%; H, 2.35%. And the powder x-ray diffraction pattern of the

72hs

150ºC

35

product matched with the calculated diffraction one generated from single crystal

structural analysis.

MOP1-2: [Ga8(H2O)4(PO4)4(HPO4)4(C2O4)4](H4APPIP)(H2O)4 was prepared

starting from a mixture containing Ga2O3, HNO3 (6M), H3PO4, H2C2O4·2H2O, APPIP,

and H2O in a molar ratio of 1:12:4:2:2:400.

Ga2O3 + 12 HNO3 + 4 H3PO4 + 2 H2C2O4(H2O)2 + 2 APPIP + 400 H2O

MOP1-2: [Ga8(H2O)4(PO4)4(HPO4)4(C2O4)4](H4APPIP)(H2O)4

In a typical synthesis, 0.158 g of Ga2O3 (0.84mmol) was dispersed in 4.3 mL of

water and 1.7 mL of HNO3 (6M) under stirring; 0.23 mL of H3PO4 (3.36mmol, aqueous

85 wt %), 0.2125 g of H2C2O4(H2O)2 (1.68mmol), and 0.36 mL of APPIP (1.68mmol)

were added with continuous stirring and the mixture was homogenized for ~30 min. The

pH of the starting mixture was 0.09. Then the starting mixture (~7 mL) was transferred to

a 23-mL capacity PTFE-lined stainless steel autoclave (Parr, Moline, IL) sealed and

heated at 150 °C for 72 hours under autogenous pressure followed by slow cooling to

room temperature at 10 °C/h. The pH of the mixture after reaction was 1.60. The

resulting product, which consisted of colorless plate-shaped crystals of MOP1-2 obtained

in 60% yield based on gallium, was filtered and washed with deionized water and acetone

and dried in air. Elemental analysis confirmed the number of tetra-protonated APPIP,

oxalates, and water molecules per formula unit. Calcd: C, 10.89%; N, 2.82%; H, 2.23%.

Found: C, 9.84%; N, 2.60%; H, 2.88%. The purity of the product was confirmed by

72hs

150ºC

36

recording the powder x-ray diffraction pattern, which matched the calculated diffraction

pattern generated from single crystal structural analysis.

3.3.2 Crystal structure determination

Colorless single crystals of these two compounds were selected for single crystal

X-ray crystallographic analysis. Three-dimensional X-ray diffraction intensity data were

measured at 198(2) K for MOP1-1 and 163(2) K for MOP1-2 on a Bruker P4

diffractometer system equipped with a graphite monochromator and a Mo Kα fine-focus

sealed tube (λ = 0.71073 Å) operated at 1.5KW power (50 kV, 30mA). Data were

corrected for absorption effects using the multi-scan technique (SADABS) and the

structures were solved and refined using full-matrix least-squares techniques (Bruker

AXS SHELXTL). The positional parameters for all the atoms were determined using

direct methods. The Ga and P atoms were located first, and the C, O, N, and H atoms

were found from successive difference Fourier maps. Details of data collection and

structure refinement are summarized in Table 3.1.

37

Table 3.1 Crystallographic Data of MOP1-1 and MOP1-2

MOP1-1 MOP1-2

Formula [Ga4(PO4)4(H2PO4)(C2O4)]

(C4N3H15)(H2O)2.5

[Ga8(H2O)4(PO4)4(HPO4)4

(C2O4)4](C10N4H28)(H2O)4

Formula weight 994.1 2022.1

Temperature 198(2) K 163(2) K

Wavelength 0.71073 Å 0.71073 Å

Crystal system Monoclinic Orthorhombic

Space group C2/c (No. 15) Pccm (No. 49)

Unit cell dimensions

a = 20.155(7) Å

b = 15.725(6) Å

c = 9.079(4) Å

β = 106.11(3)°

a = 10.044(2) Å

b = 11.728(3) Å

c = 12.385(3) Å

Volume 2764.7(19) Å3 1459.1(6) Å3

Z 8 4

Density (calculated) 2.267 Mg/m3 2.445 Mg/m3

Absorption coefficient 4.253 mm-1 4.006 mm-1

F(000) 1848 1070

Crystal size (mm3) 0.2 x 0.2 x 0.02 0.3 x 0.3 x 0.03

Theta range for data

collection 2.62 to 25.35°. 3.14 to 30.19°.

Index ranges -24 ≤ h ≤ 24, -18 ≤ k ≤ 18,

-10 ≤ l ≤ 10

-13 ≤ h ≤ 13, -16 ≤ k ≤ 16,

-17 ≤ l ≤ 17

Reflections collected 5183 4468

38

Independent reflections 2523[R(int) = 0.0789] 2247 [R(int) = 0.0741]

Completeness to theta 99.6% to 25.35° 99.2% to 30.19°

Absorption correction SADABS SADABS

Refinement method Full-matrix least-squares on F2 Full-matrix least-squares on F2

Data / restraints /

parameters 2523 / 0 / 200 2247 / 2 / 138

Final R indices

[I>2sigma(I)]a,b

R1 = 0.0559,

wR2 = 0.1088

R1 = 0.0398,

wR2 = 0.0781

R indices (all data)a,b R1 = 0.1047,

wR2 = 0.1248

R1 = 0.0680,

wR2 = 0.0860

Goodness-of-fitc on F2 1.011 1.028

Largest diff. peak and hole 0.797 and -1.135 e.Å-3 0.746 and -0.736 e.Å-3

a R1 = Σ ||Fo| - |Fc|| / Σ |Fo|

b wR2 = [ Σ [w(Fo2-Fc2)2] / Σ [w(Fo2)2]1/2, where w = 1 / [σ2(Fo2) + (aP)2 + bP], P =

(max(Fo2, 0) +2Fc2)/3.

c GooF = [Σ [w(Fo2 - Fc2)2] / (Nobs - Nparameter)]1/2

39

The most important bond lengths and angles of compounds MOP1-1 and MOP1-2

are given in Tables 3.2 and 3.3.


MOP1-1: [Ga4(PO4)4(H2PO4)(C2O4)]( C4N3H15)(H2O)2.5

Ga(1)O6 Octahedron Ga(2)O4 Tetrahedron Oxalate Linker

Ga(1)-O(1) 1.937(6) Ga(2)-O(7) 1.801(7) C(1)-O(5) 1.259(10)

Ga(1)-O(2) 1.919(6) Ga(2)-O(8) 1.824(7) C(1)-O(6) 1.243(10)

Ga(1)-O(3) 1.933(6) Ga(2)-O(10) 1.818(6) C(1)-C(1)#5 1.535(16)

Ga(1)-O(4) 1.940(6) Ga(2)-O(11) 1.803(6)

Ga(1)-O(5) 2.045(6)

Ga(1)-O(6) 2.070(5)

P(1)O4 Tetrahedron P(2)O4 Tetrahedron H2P(3)O4 Tetrahedron

P(1)-O(4) 1.505(6) P(2)-O(1) 1.511(6) P(3)-O(2) 1.519(6)

P(1)-O(7) 1.532(6) P(2)-O(3) 1.508(6) P(3)-O(2)#3 1.519(6)

P(1)-O(8) 1.533(6) P(2)-O(10) 1.543(6) P(3)-O(12) 1.515(10)

P(1)-O(9) 1.515(7) P(2)-O(11) 1.549(6) P(3)-O(12)#3 1.516(10)

P-O-Ga Inter-polyhedra Bond Angles O(12)-H(12) 0.93(1)

P(2)#4-O(1)-Ga(1) 137.9(4) P(1)-O(7)-Ga(2)#1 136.8(4) O(12) #3-H(12) #3 0.93(1)

P(3)-O(2)-Ga(1) 141.9(4) P(1)-O(8)-Ga(2) 129.1(4)

P(2)-O(3)-Ga(1) 151.6(4) P(2)-O(10)-Ga(2) 132.3(4)

P(1)-O(4)-Ga(1) 144.7(4) P(2)-O(11)-Ga(2)#4 128.6(4)

Symmetry transformations used to generate equivalent atoms:

#1 -x+1/2,-y+1/2,-z+1; #3 -x+1,y,-z+1/2; #4 x,-y+1,z-1/2; #5 -x+1/2,-y+1/2,-z.

40


MOP1-2: [Ga8(H2O)4(PO4)4(HPO4)4(C2O4)4](C10N4H28)(H2O)4

Ga(1)(H2O)O5 Octahedron Ga(2)O6 Octahedron Oxalate Linker

Ga(1)-O(1) 1.931(3) Ga(2)-O(2) 1.908(2) C(1)#5-O(6) 1.256(6)

Ga(1)-O(1)#1 1.931(3) Ga(2)-O(2) #2 1.908(2) C(1)-O(7) 1.258(6)

Ga(1)-O(3) 1.906(4) Ga(2)-O(4) 1.910(3) C(2)-O(8) 1.241(3)

Ga(1)-O(6) 2.082(4) Ga(2)-O(4) #2 1.910(3) C(2)-O(8)#6 1.241(3)

Ga(1)-O(7) 2.038(4) Ga(2)-O(8) 2.081(2) C(1)-C(1)#5 1.535(12)

Ga(1)-O(9) 1.951(4) Ga(2)-O(8) #2 2.081(2) C(2)-C(2)#7 1.564(9)

O(9)-H(9O) 0.75(6)

P(1)O4 Tetrahedron HP(2)O4 Tetrahedron P-O-Ga Inter-polyhedra Bond

Angles

P(1)-O(1) 1.540(3) P(2)-O(3)#4 1.518(4) P(1)-O(1)-Ga(1) 139.82(16)

P(1)-O(1)#3 1.540(3) P(2)-O(4) 1.503(3) P(2)#4-O(3)-Ga(1) 132.3(3)

P(1)-O(2) 1.530(3) P(2)-O(4)#1 1.503(3) P(1)-O(2)-Ga(2) 146.11(18)

P(1)-O(2)#3 1.530(3) P(2)-O(5) 1.565(4) P(2)-O(4)-Ga(2) 150.82(18)

O(5)-H(5O1) 0.84(2)

O(5)-H(5O2) 0.85(2)

Symmetry transformations used to generate equivalent atoms:

#1 x,y,-z; #2 x,-y,-z+1/2; #3 -x,y,-z+1/2; #4 -x,-y,-z; #5 -x,-y+1,-z; #6 -x+1,y,-z+1/2; #7

-x+1,-y,z

41

3.3.3 Results and discussion

Crystal structure description:

MOP1-1: [Ga4(PO4)4(H2PO4)(C2O4)](H3DETA)(H2O)2.5 has a 3D

framework that is made up of inorganic gallium phosphate tubes filled with disordered

SDA molecules (DETA) along (c) axis and cross-linked via organic oxalate ligands. The

hybrid framework generates 9×9 Å2 channels containing water molecules along the (c)

axis (Figure 3.2).

Figure 3.2 Projection of 3D framework of MOP1-1 along (c) axis showing the inorganic

gallium phosphate tubes bridged by oxalate ligands

Gallium phosphate Tube Oxalate linker

Water molecules

Disordered SDA

42

Figure 3.3 Fragment of the structure of MOP1-1 showing tetramer connectivity

The tube consists of Ga2O2(PO4)2 tetramers made of two Ga(2)O4 tetrahedra and

two P(1)O4 tetrahedra linked through O(7) and O(8) (Figure 3.3). And this tetramer binds

Ga(1)O6 octahedra through two PO4 tetrahedra to form a helical chain. Each chain is

connected to another by H2P(3)O4 tetrahedra in the direction of the (a) axis to form an

inorganic tube filled with disordered SDA molecules. The inorganic tubes are connected

to each other by bridging oxalates to form wave-like sheets along the (b) direction.

The octahedral gallium atom Ga(1) is coordinated by two oxygens O(5) and O(6)

from a bidentate oxalate ligand, three oxygen atoms from three coordinating phosphate

Ga2O2(PO4)2 tetramer

43

tetrahedra (two P(2)O4, and one P(1)O4), and one oxygen from the H2P(3)O4 tetrahedron.

The bis-bidentate coordination by the oxalate ligand results in a distorted octahedron for

Ga(1), as indicated by a longer Ga-O bond: Ga(1)−O(5) = 2.045(6) Å and Ga(1)−O(6) =

2.070(5) Å. The other four Ga-O bonds with PO4 tetrahedra have similar lengths and

range from 1.919(6) to 1.940(6) Å. Ga(2)O4 tetrahedron coordinates two P(2)O4 and two

P(1)O4 tetrahedra at the same time with shorter Ga-O bond distance from 1.801(7) to

1.824(7) Å (Figure 3.4).

Three different coordinating phosphate groups are present: P(1)O4 shares one

oxygen with the Ga(1)O6 octahedron through O(4) and two oxygen atoms with GaO4

tetrahedra. P(2)O4 shares all its oxygens with gallium atoms: two with the tetrahedral

Ga(2) atom and two with octahedral Ga(1). H2P(3)O4 links two identical Ga(1)O6

octahedra by O(2). The other two oxygens O(12) correspond to an OH groups with

O(12)−H(12) = 0.93(1) Å.

Figure 3.4 Environments around Ga(1) and Ga(2) atoms in MOP1-1

44

MOP1-2: [Ga8(H2O)4(PO4)4(HPO4)4(C2O4)4](H4APPIP)(H2O)4 has a 3D

porous framework built up of gallium phosphate inorganic tubes along (c) axis linked to

each other by oxalate ligands in both (a) and (b) directions. The framework generates 9×9

Å2 one dimensional channels along the (c) axis containing disordered protonated amine

[H4APPIP]4+ (Figure 3.5).

Figure 3.5 Perspective view along (c) axis of 3D framework of MOP1-2

The gallium phosphate tube is formed of repeating secondary building units (SBU)

containing four GaO6 octahedra linked with four PO4 tetrahedra through corner sharing.

Two types of oxalate anions coordinate with two crystallographic independent gallium

octahedra along (a) and (b) directions, respectively (Figure 3.6).

Channel containing disordered template

Oxalate linker

Gallium phosphate Inorganic tube

45

Figure 3.6 Connectivity of gallium phosphate tubes along (a) and (b) axis

There are two crystallographically independent oxalate anions. Along (a) axis

oxalate (2) bridges two Ga(2)O6 octahedra through O(8). Ga(2) is coordinated by two

HP(2)O4, two P(1)O4 groups and one bis-bidentate coordinated oxalate ligand resulting in

a distorted octahedron, as indicated by a wide range of Ga(2)−O bond lengths

1.908(2)−2.081(2) Å and a small bond angle O(8)−Ga(2)−O(8) = 79.06(13)°.

Along the (b) axis the oxalate (1) bridges two Ga(1)O6 octahedra through O(6)

and O(7). Ga(1) is coordinated by one HP(2)O4, two P(1)O4 groups, one bis-bidentate

coordinated oxalate ligand and one water molecule, also form a distorted octahedron, as

Rotate 90˚

SBUs

Bridging Oxalate (2) Bridging Oxalate (1)

46

indicated by a wide range of Ga(1)−O bond lengths 1.906(4)−2.082(4) Å and a small

bond angle O(6)−Ga(2)−O(7) = 80.96(15)° (Figure 3.7).

Two different coordinating phosphate groups are present: HP(2)O4 shares one

oxygen with Ga(1)O6 octahedron through O(3) and two oxygens O(4) with two Ga(2)O6

octahedra. The fourth oxygen O(5) corresponds to an OH group with long bond P(2)−O(5)

= 1.565(4) Å. The hydrogen of HP(2)O4 group is disordered over two positions (50%

each). P(1)O4 shares all four oxygens with gallium atoms: two identical Ga(1)O6

octahedra by O(1) and two identical Ga(2)O6 octahedra by O(2).

Figure 3.7 Environments around Ga(1) and Ga(2) atoms in MOP1-2

47

Thermal stability:

The thermal stabilities of compound MOP1-1 and MOP1-2 were investigated by

thermogravimetric analysis (TGA). They showed similar weight loss under O2 and under

N2 in the temperature range 30−800 °C.

Two distinct weight losses are observed for MOP1-1 (Figure 3.8). The first

weight loss (5.5%) occurs between 100 and 250 °C and corresponds to the loss of 2.5

H2O (calcd 4.5%). The second weight loss (17.5%) occurs between 250 and 800 °C and

corresponds to the loss of the oxalates and the amine, leading to the formation of gallium

phosphate (calcd 19.5%).

[Ga4(PO4)4(H2PO4)(C2O4)](H3DETA)(H2O)2.5

[Ga4(PO4)4(H2PO4)(C2O4)](H3DETA) GaPO4

Figure 3.8 TGA of compound MOP1-1

Step 1

-2.5 H2O

Step 2

- (H3DETA+C2O4)

Step 1

Step 2

48

For compound MOP1-2, there are two different water molecules in the structure.

One of them acts as an aquo ligand to gallium atoms and is more difficult to remove. As

shown in Figure 3.9, the first weight loss (4.5%) occurs between 50 and 125 °C and

corresponds to the loss of 4 H2O in the channels of the structure (calcd 3.6%). The second

loss (5.0%) occurs between 125 and 200 °C corresponds to the rest 4 coordination water

(calcd 3.6%). X-ray diffraction studies of a single crystal selected from the sample after

heating at 125 °C confirmed the loss of the water molecules in the channels and the

stability of the framework. The loss of water results in a slight change in the unit cell

parameters with a decrease of 135.1 Å3 in cell volume (orthorhombic, a = 9.818(7) Å, b =

10.9990(7) Å, c = 12.268(6) Å, V = 1324(2) Å3; fresh one: orthorhombic, a = 10.044(2))

Å, b = 11.728(3) Å, c = 12.385(3) Å, V = 1459.1(6) Å3). The compound loses water of

coordination at about 200 ºC and the framework is destroyed. The third weight loss

(23.0%) occurs between 200 and 800 °C and corresponds to the loss of the oxalates and

the amine, leading to the formation of gallium phosphate (calcd 28.0%).

[Ga8(H2O)4(PO4)4(HPO4)4(C2O4)4](H4APPIP)(H2O)4

[Ga8(H2O)4(PO4)4(HPO4)4(C2O4)4](H4APPIP)

[Ga8(PO4)4(HPO4)4(C2O4)4](H4APPIP) GaPO4

Step 1

-4 H2O

Step 3

- (H4APPIP+C2O4)

Step 2

-4 H2O

49

Figure 3.9 TGA of compound MOP1-2

Step 1

Step 3

Step 2

50

3.4 Indium phosphate oxalates

Indium is a bigger group 13 metal atom and can only be six coordinated. When this

heavier element was used instead of gallium, two novel indium phosphate oxalates were

obtained. MOP1-3: [In6(HPO4)8(C2O4)3](H4APPIP) has a 3D framework formed of

inorganic indium phosphate layers parallel to the (ab) plane linked by oxalate ligands

along the (c) axis. The hybrid framework generates 10×10 Å2 cross section channels

containing protonated (H4APPIP)4+ cations. No water or other solvent molecules are

found in the structure. Under higher pH of starting solution, we made MOP1-4:

[In4(HPO4)6(C2O4)2](H4APPIP)(H2O)2. This compound also has a 3D framework

formed of inorganic indium phosphate chains along the (a) axis linked by oxalate ligands.

The hybrid framework generates smaller 6×6 Å2 channels containing protonated

(H4APPIP)4+ cations along the (a) axis.

3.4.1 Hydrothermal synthesis

MOP1-3: [In6(HPO4)8(C2O4)3](H4APPIP) was prepared starting from a mixture

containing In2O3, HNO3 (3M), H3PO4, H2C2O4·2H2O, APPIP, and H2O in a molar ratio of

1:12:4:2:2:400.

In2O3 + 12 HNO3 + 4 H3PO4 + 2 H2C2O4(H2O)2 + 2 APPIP + 400 H2O

MOP1-3: [In6(HPO4)8(C2O4)3](H4APPIP)

In a typical synthesis, 0.234 g of In2O3 (0.84 mmol) was dispersed in 2.6 mL of

water and 3.4 mL of HNO3 (3M) with stirring; 0.23 mL of H3PO4 (3.36 mmol, aqueous

72hs

150ºC

51

85 wt %), 0.2125 g of H2C2O4(H2O)2 (1.68 mmol), and 0.36 mL of APPIP (1.68 mmol)

were added with continuous stirring and the mixture was homogenized for ~30 min. The

pH of the starting mixture was 0.70. The starting mixture (~7 mL) was transferred to a

23-mL capacity PTFE-lined stainless steel autoclave (Parr, Moline, IL) sealed and heated

at 150 °C for 72 hours under autogenous pressure followed by slow cooling to room

temperature at 10 °C/h. The pH of the mixture after reaction was found to be 2.67. The

resulting product, which consisted of colorless needle-shaped crystals of MOP1-3

obtained in 63% yield based on indium, was filtered and washed with deionized water

and acetone and dried in air. Elemental analysis confirmed the number of tetra-protonated

APPIP and oxalates per formula unit. Calcd: C, 9.98%; N, 4.23%; H, 1.88%. Found: C,

10.14%; N, 4.20%; H, 2.30%. And the powder x-ray diffraction pattern of the product

matched well with the calculated diffraction pattern generated from single crystal


MOP1-4: [In4(HPO4)6(C2O4)2](H4APPIP)(H2O)2 was prepared starting from a

mixture containing In2O3, HCl (3M), H3PO4, H2C2O4·2H2O, APPIP, and H2O at a molar

ratio of 1:6:4:2:2:333.

In2O3 + 6 HCl + 4 H3PO4 + 2 H2C2O4(H2O)2 + 2 APPIP + 333 H2O

MOP1-4: [In4(HPO4)6(C2O4)2](H4APPIP)(H2O)2

In a typical synthesis, 0.278 g of In2O3 (1 mmol) was dispersed in 4 mL of water

and 2 mL of HCl (3M) with stirring; 0.46 g of H3PO4 (4 mmol, aqueous 85 wt %), 0.252

72hs

150ºC

52

g of H2C2O4(H2O)2 (2 mmol), and 0.413 g of APPIP (2 mmol) were added with

continuous stirring and the mixture was homogenized for ~30 min. The pH of the starting

mixture was 1.12. Then the starting mixture (~7 mL) was transferred to a 23-mL capacity

PTFE-lined stainless steel autoclave (Parr, Moline, IL) sealed and heated at 150 °C for 72

hours under autogenous pressure followed by slow cooling to room temperature at 10

°C/h. The pH of the mixture after reaction was found to be 1.20. The resulting product

consisted of colorless stick-shaped crystals of MOP1-4, obtained in 40% yield based on

indium, which was filtered and washed with deionized water and acetone, then dried in

air. Elemental analysis confirmed the number of tetra-protonated APPIP, oxalates, and

water molecules per formula unit. Calcd: C, 11.58%; N, 3.86%; H, 2.64%. Found: C,

10.56%; N, 3.66%; H, 2.88%. The powder x-ray diffraction pattern of the product

matched well with the calculated diffraction pattern generated from single crystal


3.4.2 Crystal structure determination

Colorless single crystals of these two compounds were selected for single crystal

X-ray crystallographic analysis. X-ray intensity data were measured at 293(2) K for

MOP1-3 and 193(2) K for MOP1-4 on a Bruker Smart Apex CCD area detector system

equipped with a graphite monochromator and a Mo Kα fine-focus sealed tube (λ =

0.71073 Å) operated at 1.5KW power (50kV, 30mA). Data were corrected for absorption

effects using the multi-scan technique (SADABS) and the structures were solved and

refined using full-matrix least-squares techniques (Bruker AXS SHELXTL). The

positional parameters for all the atoms were determined using direct methods. The In and

53

P atoms were located first, and the C, O, N, and H atoms were found from successive

difference Fourier maps. Details of data collection and structure refinement are

summarized in Table 3.4.

Table 3.4 Crystallographic Data of MOP1-3 and MOP1-4

MOP1-3 MOP1-4

Formula [In6(HPO4)8(C2O4)3](C10N4H28) [In4(HPO4)6(C2O4)2](C10N4H28)

(H2O)2

Formula weight 1925.16 1451.58

Temperature 293(2) K 193(2) K

Wavelength 0.71073 Å 0.71073 Å

Crystal system Trigonal Monoclinic

Space group P-3c1 (No. 165) P21/n (No. 14)

Unit cell dimensions a = 14.004(2) Å

b = 15.191(3) Å

a = 13.275(2) Å

b = 10.810(1) Å

c = 14.209(2) Å

β = 112.849(2)°

Volume 2580.0(7) Å3 1878.9(4 Å3

Z 2 4

Density (calculated) 2.478 Mg/m3 2.566 Mg/m3

Absorption coefficient 3.032 mm-1 2.805 mm-1

F(000) 2160 1416

Crystal size (mm3) 0.20 x 0.06 x 0.02 0.14 x 0.11 x 0.05

54

Theta range for data

collection 2.68 to 30.57°. 3.83 to 30.51°.

Index ranges -16 ≤ h ≤ 19, -19 ≤ k ≤ 19,

-18 ≤ l ≤ 21

-18 ≤ h ≤ 18, -15 ≤ k ≤ 15,

-19 ≤ l ≤ 20

Reflections collected 26116 19326

Independent reflections 2368[R(int) = 0.0808] 5595 [R(int) = 0.0452]

Completeness to theta 89.3% to 30.57° 97.4% to 30.51°

Absorption correction SADABS SADABS

Refinement method Full-matrix least-squares on F

Documents

PHOSPHATE HYBRID-FRAMEWORK MATERIALS By YUE ZHAO … · 2013. 5. 8. · new MOP materials with novel structures. They show a great diversity of structural topologies, coordination