Chapter 7 Interaction of Lewis-bases with Polymeric …shodhganga.inflibnet.ac.in/bitstream/10603/7190/13/13...Interaction of Lewis-bases with Polymeric Metal Oxalates 315 (a) Nickel(II)

Chapter 7

Interaction of Lewis-bases with Polymeric Metal(II) Oxalates

7.1

xalic acid, (H

Introduction

2ox), HOOC-COOH, can be considered as the

simplest of all dicarboxylic acids. The structure involves

simply two -COOH groups connected directly through the

two carboxyl carbon atoms and has got unique electronic structure

quite different from that of both succinic (H2suc) and malonic

(H2mal) acids. Not only this molecule lacks any spacer function

between the carboxylic groups but also it has got connectivity

through two sp2 hybridized C atoms. Consequently its dianion,

-OOC-COO-, has conjugation extended over all the 6 atoms forming

a perfect planar configuration. This is one main feature that

distinguishes the oxalate moiety from its counterparts mentioned

in earlier chapters. Though, in principle, oxalate moiety can take

part in coordination involving various linking modes referred

earlier, the predominant ligation mode is seen to be mostly bis-

bidentate bridging type (see Chapter 1, Section 1.2, for details).

This makes the oxalate moiety a very strong bridging ligand

through σ-coordination resulting in polymeric metal carboxylates

with rigid 1D, 2D or 3D framework structures. Interesting feature

in these extended structures is the π-electron delocalisation

possible along the whole metal-oxalate framework both through pπ-

pπ and pπ-dπ interactions. Such interactions result in an effective

metal to metal electronic communication via the conjugated oxalate

function leading to interesting magnetic and electronic properties.

O

Many metal oxalate structures are reported in the

literature including those occurring naturally as minerals.(1) The

2D honey-comb(2,3) structure is seen to be the most common for the

oxalates which allows for large variations in molecule type and pore

Chapter 7 312

functionalization. The 1D coordination polymer NH4[Ti(ox)2].2H2O is

seen to contain the cyclic tetranuclear [Ti4O4(ox)8]8- ion units and

are used as basic building blocks.(4) The first example of an

oxalato-uranylate, Na2[(UO2)4(ox)5(H2O)2].8H2O(5) has a zeolite-type

structure. A series of open-framework oxalates containing zirconium

and cadmium or lead along with alkali-metal or ammonium cations

have also been reported.(6) These compounds contain MO8

polyhedral units that are linked through oxalate oxygen atoms to

give 3D open frameworks. In (NH4)2[CdZr(ox)4].3.9H2O and

[H3N(CH2)2NH3][CdZr(ox)4].4.4H2O, right-handed metal-oxalate

helical wires are formed through connectivity between the oxalate

ions and the MO8 polyhedra (M = Cd, Zr).(6a) The oxalate unit serves

to link the chains together to yield a 3D structure with channels.

Tamaki and co-workers have prepared 2D mixed-metal oxalates

with CrIII centers.(7) The [Cr(ox)3]3- ion acts as a building block by

binding to three MII centers (M = Fe, Co, Ni, Cu and Zn) ions through

oxalate-ion bridges, forming an extended network. An interesting

ion-pair [Cu(bipy)2(CH3COO)]+[Cu(bipy)2Cr(ox)3]-.10.5H2O(8) has been

reported as the first compound containing the [Cr(ox)3]3- units as

monodentate ligands. These complexes form examples in the design

and tuning of molecular components in extended structures to

attain desirable properties. Recently Arco et al(9) has reported the

intercalation of [Cr(ox)3]3- complexes in Mg, Al layered double

hydroxides. Mixed-valent oxalates A[MII-MIII(ox)3] (A = monocation;

MII = Mn, Fe, Co, Ni, Cu and Zn; MIII= Cr, Fe and Co) have

distinct magnetic properties, varying from paramagnetic to

ferromagnetic or antiferromagnetic.(10-15) Chiral metal complexes

have also been made use of to form layered magnets with oxalate

networks and 3D anionic networks as in [(ZII(bipy)3)[MIMIII(ox)3]] or

Interaction of Lewis-bases with Polymeric Metal Oxalates 313

[(ZII(bipy)3)(MIIMIII(ox)3)] (bipy = 2,2'-bipyridyl; ZII = Fe, Co, Ni, Ru and

Zn; MI = alkali metal, NH4+; MII = Mn, Fe, Co and Cu; MIII = Cr

and Fe).(16) Other interesting 2D ternary complexes reported are

[Cu(ox)(L)(H2O)].nH2O(17) (L = bipy, phen and n-phen; n = 1, 2),

[M(ox)L]n(18) [L = 4,4'-bipy; M = Co(II), Fe(II), Ni(II) and Zn(II)) and

[M(ox)(L)2].nH2O(19) (n = 4,5; M = Ni, Cu; L = bipy or phen) in

which the oxalate anions are found to function as bidentate

bridging moieties. In [Cu(bipy(ox)].2H2O,(20) the oxalate anions

are centrosymmetric and act as quadridentate bridging ligands

resulting in zigzag polymeric structure whereas

[Cu2(bipy)2(H2O)2(NO3)2(ox)](21) has the unusual ligand arrangement

and the packing of molecules are attributed to intermolecular and

intramolecular hydrogen bonding leading to a zigzag chain which

exhibits antiferromagnetism. In [Cu(en)2][Cu(ox)2],(20a) the oxalate anions

act as tridentate moieties. The 1D complex, {[Cu(bipy)(ox)]2.5H2O}n(22)

consists of columnar stacks of neutral [Cu(ox)(bipy)] units, exhibiting

alternating ferro-antiferromagnetic interactions. The 3D supramolecular

complex, K[Cu(trans[14]dien)][Cr(ox)3](23) has been reported, which

has large helical tunnels that are formed by the oxalate-bridged,

octahedrally coordinated Cr and K centers. In the iron oxalate,

(NH4)2[Fe2O(ox)2Cl2].2H2O,(24) a 3D structure with helical tunnels

occupied by guest species has been reported. In the iron(III)

system, [(acac)2Fe(ox)Fe(acac)2], Fujino et al(25) reported the

stabilization of Fe(III) to Fe(II) mixed valence state by the electronic

delocalisation through the oxalate bridge. A hydrothermally

prepared 1D oxalate, Na2[Co2(ox)3(H2O)2],(26) is known to possesses

a ladder-like topology, which manifests antiferromagnetic

ordering. An interesting sheet like polymeric complex,

[NaCr(bipy)(ox)2(H2O)].2H2O has been reported by Munoz et al(27)

Chapter 7 314

and observed that oxalate ligands function as monodentate as well

as bis-chelating within the chain, showing antiferromagnetic

property. On the other hand, Ba4[{Fe(ox)(OH)}4(ox)Cl2](28) possesses

two distinct channels (concave and convex) formed by the linking

of vertex-sharing FeO6 octahedra through -OH bridges and oxalate

ions in a monodentate fashion. Recently Pointillart et al(29) has

reported an interesting three-dimensional oxalate-based complexes,

{[Ru(bipy)3][Cu2xNi2(1-x)(ox)3]}n (0 ≤ x ≤ 1) where Cu(II) has unusual

tris(bischelated) environment and the compounds are found to be

isostructural, single-phased and at low temperature seen to exhibit

long-range ordered magnetic behaviour. Several cyanogold

complexes react with the binuclear nickel complex,

[{Ni(dien)(H2O)}2(ox)](PF6)2.2H2O(30) resulting in a variety of di- or

polynuclear compounds which show antiferromagnetic behaviour.

The use of metal oxalate complexes of Cr, Fe, Mn, Co and Al as

novel inorganic dopants is well documented.(31) In the present study

we discuss in detail the interaction of Lewis-bases with polymeric

metal oxalates and formation and characterisation of various mixed

ligand complexes.

7.2 Experimental

7.2.1 Preparation of oxalate complexes of divalent metal ions

Metal oxalates of Ni(II), Co(II) and Cu(II) were prepared by

reacting the appropriate metal carbonate with a hot aqueous

solution of oxalic acid in stoichiometric quantities. The complexes

were separated by filtration. These were washed repeatedly with hot

water and methanol and dried under vacuum over P2O5.


(a) Nickel(II) oxalate complex, [Ni(H2O)2(ox)]n, 40

To an aqueous solution of oxalic acid (0.13g, 1mM), nickel

carbonate (0.37g, 1mM) was added slowly with stirring. Brisk

effervescence formed indicating the complex formation. The

reaction mixture was boiled on a steam bath for about 30 min. The

amount of nickel carbonate added was slightly less than the

stoichiometric amount of oxalic acid. The light green complex

formed was filtered and washed repeatedly with hot water to

remove any excess acid present and finally with methanol. The

pure complex thus obtained was dried in vacuo. (yield : 90%)

(b) Cobalt(II) oxalate complex, [Co(H2O)2(ox)]n, 41

Cobalt carbonate (0.11g, 1mM) was added in small quantity

with stirring to a hot aqueous solution of oxalic acid (0.13g, 1mM).

The reaction mixture was boiled on a steam bath for about 1h. The

rose complex formed was filtered and washed repeatedly with hot

water to remove any excess acid present and finally with methanol.

The pure complex thus obtained was dried in vacuo. (yield : 90%)

(c) Copper(II) oxalate complex [Cu(ox)]n, 42

The procedure adopted for the preparation of copper(II)

oxalate complex was almost the same as that of nickel(II) or

cobalt(II) complex. About 0.23g (1mM) of cupric carbonate was

added in small quantity to a hot aqueous solution of 0.13g (1mM)

oxalic acid while stirring. The light blue complex formed was

filtered and washed repeatedly with hot water to remove excess

acid and finally with methanol. It was dried under vacuum over

P2O5. (yield : 85%)

Chapter 7 316

7.2.2 Preparation of Lewis-base adducts of nickel(II) oxalate

(a) [Ni(en)(ox)]n, 43

A solution of en (0.19ml, 3mM) in methanol was added

dropwise to a suspension of nickel(II) oxalate (0.18g, 1mM) in

methanol with constant stirring for about 2 h. The complex gets

separated out as rose violet solid. This was filtered and was

repeatedly washed with ether and dried in vacuo. (yield : 80%)

(b) [Ni(bipy)(ox)]n, 44

A solution of 2,2'-bipy (0.47g, 3mM) in methanol was added


methanol. The mixture was kept under reflux for about 2 h. The

complex separated out as light violet solid was filtered. This was

repeatedly washed with ether and dried under vacuum over P2O5.

(yield : 80%)

(c) [(Ni(phen)(ox)).2H2O]n, 45

A solution of 1,10-phen (0.6g, 3mM) in methanol was added


methanol. The mixture was kept under reflux for about 2 h. The

complex separated out as light violet solid was filtered. This was

washed with methanol followed by ether which was then dried in

vacuo. (yield :75%)

(d) [Ni(py)2(ox)]n, 46

An excess of pyridine was added to a nickel(II) oxalate

(0.36g, 1mM) suspension in methanol with constant stirring. The

reaction mixture was refluxed for about 2 h. The complex separated


out as light green solid was filtered and repeatedly washed with

methanol followed by ether. This was dried in vacuo. (yield :75%)

(e) [(Ni(pn)(ox)).H2O]n, 47

A solution of pn (0.27ml, 3mM) in methanol was added


methanol with constant stirring for about 2 h. A clear blue solution

was obtained from which solid blue complex was seen to be

separating out soon, making the supernatant liquid colourless. The

solid complex was filtered and repeatedly washed with methanol

followed by acetone. This was dried in vacuo. (yield : 80%)

7.2. 3 Preparation of Lewis-base adducts of cobalt(II) oxalate

(a) [(Co(en)(ox)).H2O]n, 48

A solution of en (0.19ml, 3mM) in methanol was added to a

suspension of cobalt(II) oxalate (0.18g, 1mM) in methanol with

constant stirring followed by refluxing for about 2 h. The complex

separated out as brown solid was filtered and repeatedly washed with

methanol followed by ether. This was dried in vacuo. (yield : 80%)

(b) [Co(bipy)(ox)]n, 49

To a suspension of cobalt(II) oxalate (0.18g, 1mM) in

methanol, a solution of 2,2'-bipy (0.47g, 3mM) in methanol was

added. The reaction mixture was kept under reflux for about

2 h. The complex separated out as orange solid was filtered.

This was repeatedly washed with methanol followed by ether.

This was then dried in vacuo. (yield : 80%)

Chapter 7 318

(c) [(Co(phen)(ox)).H2O]n, 50

A solution of phen (0.6g, 3mM) in methanol was added to a

suspension of cobalt(II) oxalate (0.18g, 1mM) in methanol. The

mixture was kept under reflux for about 2 h. The complex separated

out as orange solid was filtered and repeatedly washed with methanol

followed by ether. This was dried in vacuo. (yield : 85%)

(d) [Co(py)2(ox)]n, 51

An excess of pyridine was added to a cobalt(II) oxalate

(0.36g, 1mM) suspension in methanol with constant stirring. The

reaction mixture was refluxed for about 2 h. The complex

separated out as light pink solid was filtered and repeatedly

washed with methanol followed by diethyl ether. It was dried in

vacuo. (yield : 75%)

(e) [Co(pn)(ox)]n, 52


dropwise to a suspension of cobalt(II) oxalate (0.36g, 1mM) in

methanol with constant stirring for about 2 h. The complex was

separated out as dark pink solid which was filtered and repeatedly

washed with methanol followed by acetone. This was dried in

vacuo.(yield : 85%)

7.2.4 Preparation of Lewis- base adducts of copper(II) oxalate

(a) [(Cu(en)(ox)).2H2O]n, 53

A solution of en (0.19ml, 3mM) in methanol was added

dropwise to a suspension of copper(II) oxalate (0.15g, 1mM) in

methanol with constant stirring for about 1 h. The complex separated


out as violet solid was filtered and repeatedly washed with methanol

followed by ether. This was dried in vacuo. (yield : 80%)

(b) [Cu(bipy)(ox)]n, 54

To a suspension of copper(II) oxalate (0.15g, 1mM) in

methanol , a solution of bipy (0.47g, 3mM) in methanol was added.

The mixture was kept under reflux for about 2 h. The complex

separated out as light blue solid was filtered and repeatedly washed

with methanol followed by ether. Finally it was dried in vacuo.

(yield : 80%)

(c) [Cu(phen)(ox)]n, 55

The method adopted for the preparation of this compound

was almost same as that employed for the 2,2'-bipy adduct. The

complex was separated out as light blue solid which was then

filtered and repeatedly washed with methanol followed by ether.

This was dried in vacuo. (yield : 80%)

(d) [Cu(py)2(ox)]n, 56

An excess of pyridine was added to a copper(II) oxalate (0.15g,

1mM) suspension in methanol with constant stirring. The reaction

mixture was refluxed for about 2 h. The complex separated out as

light blue solid was filtered and repeatedly washed with methanol

followed by diethyl ether. It was then dried in vacuo. (yield : 80%)

(e) [Cu(pn)(ox)]n, 57


dropwise to a suspension of copper(II) oxalate (0.30g, 1mM) in

methanol with constant stirring for about 1 h. A clear dark blue

Chapter 7 320

solution was obtained from which solid light blue complex was found

to be separating out soon making the supernatent liquid colourless.

The solid complex was filtered and repeatedly washed with methanol

followed by acetone. This was dried in vacuo. (yield : 80%)

7.3 Results and Discussion

7.3.1 Metal oxalates of Ni(II), Co(II) and Cu(II)

Like succinic acid and malonic acid, oxalic acid also forms

complexes with metals like Ni(II), Co(II) and Cu(II). The preparative

procedures employed for generating these metal oxalates were almost

same as that used for metal succinates and metal malonates which

are described in chapters 3 and 5 respectively. The analytical data

show a strict 1:1 complex (metal : ox) for all the oxalate complexes of

the divalent metal ions. (Table 7.1). The compositions of various

metal(II) oxalates were found to be [M(H2O)2(ox)]n for Ni(II) and Co(II)

and [Cu(ox)]n for the Cu(II) ion. TG analysis could confirm the extent

of water present in the complexes.

The typical carboxylate peaks νas(CO2)and νs(CO2) for the oxalic

acid are seen to occur at 1701 and 1443 cm-1 respectively. For the

present metal oxalates these two peaks are seen to occur at 1636,

1362 cm-1 for [Ni((H2O)2(ox)]n (40), 1635, 1370 cm-1 for [Co(H2O)2(ox)]n

(41) and 1649, 1364 cm-1 for [Cu(ox)]n (42) (Table 7.2). The greater

difference in νΔ of these two bands compared to νΔ (258 cm-1) of

oxalic acid indicates the bis-bidentate bridging character of the

oxalate group.(7,32-38) The C-O stretching frequencies in these

complexes are seen to occur in the range 1316-1321 cm-1 which is

typical of chelating/bridging carboxylate group. Broad peaks in the

range 3235-3250 cm-1 were seen in all the complexes (except for 42)


which are characteristic of ν(O-H) band, indicating the presence of

coordinated water in the system. It is interesting to note that νΔ is

consistent with Irving-William series.

Table 7.1 Elemental analytical data of metal(II) oxalates

Elemental content(%) obsvd (calcd) Compound

(Emp. formula) Formula weight

C H M

Colour

[Ni(H2O)2(ox)]n

(NiC2H4O6) 40 182.69 13.17 (13.14)

2.25 (2.21)

32.2 (32.1) Green

[Co(H2O)2(ox)]n

(CoC2H4O6) 41 182.93 13.15 (13.12)

2.22 (2.20)

32.3 (32.2) Rose

[Cu(ox)]n

(CuC2O4) 42 151.54 15.80 (15.84) - 42.0

(41.9) Blue

Table 7.2 Important IR spectral data of metal(II) oxalates (cm-1)

Compound ν(O-H) νas(CO2) νS(CO2) ν(C-O) νΔ ν(O-H)

H2ox 3462 1701 1443 1330 258 1625

40 3250 1636 1362 1316 274 1608

41 3235 1635 1370 1321 265 1610

42 - 1649 1364 1319 285 -

The electronic spectra of various metal(II) oxalates were

recorded in the solid state only because of the high insolubility of

the complexes. The absorption values are given in Table 7.3.

Nickel(II) oxalate (40) gave three peaks at 25310, 15600 and 10,650

Chapter 7 322

cm-1 which are typical of octahedral Ni(II).(39,40) In the case of

cobalt(II) oxalate (41), the absorption peaks were seen at 18450

and 14490 cm-1 which are characteristic of octahedral Co(II)

species.(41,42) The broad absorption band was observed for copper(II)

oxalate (42) at 13850 cm-1 which is expected for square planar

Cu(II) species.(43-45)

Table 7.3 Electronic spectral and magnetic data of metal(II) oxalates

Compound Absor. Max ν (cm-1) Assignments μeff

(BM)

[Ni(H2O)2(ox)]n

40

25310

15600

10650

3A2g(F) → 3T1g(P) ν3

3A2g(F) → 3T1g(F) ν2

3A2g(F) → 3T2g(F) ν1

2.92

[Co(H2O)2(ox)]n

41

18450

14490

4 T1g → 4T1g(P)

4T1g → 4A2g

4.57

[Cu(ox)]n

42 13850 2B1g → 2A1g 1.43

Magnetic measurements showed that all the above oxalate

complexes are paramagnetic in nature. The μeff value of nickel(II)

oxalate complexes was found to be 2.92 BM indicating that the

complex is octahedral. The room temperature μeff value of cobalt(II)

oxalate was seen to be 4.57 BM which is characteristic of

octahedral Co(II) species. The magnetic moment of copper oxalate

complex was found to be 1.43 BM which is noticeably lower than

the value expected of typical Cu(II) complexes. Both spectral and

magnetic data indicated the strict six-coordinated character for


Ni(II) and Co(II) complexes while four coordinated character for

Cu(II) complex. A comparatively low value of μeff for 42 indicates

the close proximity of Cu ions in it for a possible Cu-Cu interaction.

Based on the above observations and high insolubility the overall

structure of the metal(II)oxalate complexes could be considered as

polymeric in nature.

7.3.2 Interaction of Lewis-bases with polymeric nickel(II) oxalate

The set of Lewis-bases chosen for interaction and

depolymerisation of nickel(II) oxalate were same as those used for

the succinate and malonate systems. We have carried out the

interaction of the bases with the metal oxalates under various

reaction conditions and stoichiometric proportions as earlier. To

isolate the new structural species, also we have employed some

optimum reaction conditions. These along with some salient

features of the reaction and the nature of products isolated are

presented in Table 7.4. Unlike in the earlier cases the various

Lewis-bases do not seem to depolymerise the metal oxalates very

easily. Only pn seems to fragment the polymer skeleton as evident

from the dissolution observed. All the isolated complexes showed

1:1 (nickel oxalate: Lewis-base) composition except for py adduct

on elemental analysis (Table 7.5). The py adducts isolated in this

system are seen to have 1:2 composition.

Chapter 7 324

Table 7.4 Interaction of metal oxalates with various Lewis-bases (LB)

Metal oxalate +

LB (in MeOH)

Conditions Observation Products Separated

40 + en (1:1) stirring, RT, (2h) no observable change no stoichiometric

compound

40 + en (1:2) stirring, RT, (2h)

slight colour change from green to rose-violet

no characterisable product


colour change from green to rose violet (solution colourless)

[Ni(en)ox]n (43)

40 + bipy (1:1)

stirring under reflux, (2h) no observable change no stoichiometric

compound

40 + bipy (1:2)

stirring under reflux, (2h)

slight colour change from green to light violet

no stoichiometric compound

40 + bipy (1:3)


colour change from green to light violet (solution colourless)

[Ni(bipy)ox]n (44)

40 + phen (1:1)

stirring under reflux, (2h) no observable change no characterisable

product

40 + phen (1:2)


slight colour change from green to light violet. (incomplete reaction)


40 + phen (1:3)


colour change from green to light violet (solution colourless)

[(Ni(phen) (ox)).2H2O]n (45)

40 + py (1:1)


product

40 + py (1:2)


slight colour change from green to light green


40 + py (excess)


colour change from green to light green (solution colourless)

[Ni(py)2ox]n (46)


40 + pn

(1:1) stirring, RT, (2h) no observable change no characterisable product

40 + pn (1:2) stirring, RT, (2h) partial dissolution

(blue solution) no characterisable product

40 + pn (1:3) stirring, RT, (2h)

complete dissolution followed by blue solid separation

[(Ni(pn)(ox)).H2O]n (47)

41 + en (1:1) stirring, RT, (2h) no observable change no characterisable

product

41 + en (1:2) stirring, RT, (2h) slight colour change

from rose to brown no stoichiometric compound


colour change from green to brown (solution colourless)

[(Co(en)(ox)).H2O]n (48)

41 + bipy (1:1)


product

41 + bipy (1:2)


slight colour change from rose to orange


41 + bipy (1:3)


colour change from rose to orange (solution colourless)

[Co(bipy)ox]n (49)

41 + phen (1:1)


product

41 + phen (1:2)


slight colour change from rose to orange


41 + phen (1:3)


colour change from rose to orange (solution colourless)

[(Co(phen)(ox)).H2O]n

(50)

41 + py (1:1)


product

41+ py (1:2)


light colour change from rose to pink


41 + py (excess)


colour change from rose to light pink (solution colour less)

[Co(py)2(ox)]n (51)

41 + pn (1:1) stirring, RT, (2h) no observable change no characterisable

product

41 + pn (1:2) stirring, RT, (2h) slight colour change

from rose to pink no stoichiometric compound

41 + pn (1:3) stirring, RT, (2h)

colour change from rose to dark pink (solution colour less)

[Co(pn)(ox)]n (52)

Chapter 7 326

42 + en (1:1) stirring, RT, (2h) no observable change no stoichiometric

compound

42 + en (1:2) stirring, RT, (2h) slight colour change

from blue to violet no characterisable product


colour change from blue to violet (solution colour less)

[(Cu(en)(ox)).2H2O]n (53)

42 + bipy (1:1)


no observable change


42 + bipy (1:2)


slight colour change from blue to light blue


42 + bipy (1:3)


colour change from blue to light blue (solution colour less)

[Cu(bipy)(ox)]n (54)

42 + phen (1:1)




42 + phen (1:2)




42 + phen (1:3)



[Cu(phen)(ox)]n (55)

42 + py (1:1)




42 + py (1:2)




42 + py (excess)



[Cu(py)2(ox)]n (56)

42 + pn (1:1)

stirring, RT, (2h)



42 + pn (1:2)

stirring, RT, (2h)



42 + pn (1:3)

stirring, RT, (2h)

complete dissolution followed by light blue solid separation

[Cu(pn)(ox)]n (57)


Table 7.5 Elemental analytical data of Lewis-base adducts of metal(II) oxalates

Elemental content % obsvd (calcd) Complex

(Emp. formula) Formula Weight

C H N M

Colour

[Ni(en)(ox)]n

NiC4H8N2O4 (43)

206.69 23.20 (23.22)

3.92 (3.90)

13.55 (13.54)

28.4 (28.3)

Rose violet

[Ni(bipy)(ox)]n

NiC12H8N2O4 (44)

302.88 47.57 (47.54)

2.70 (2.66)

9.20 (9,24)

19.4 (19.3)

Light violet

[(Ni(phen)(ox)).2H2O]nNiC14H14N2O7

(45) 380.92 44.15

(44.10) 3.72 (3.70)

7.34 (7.35)

15.5 (15.4)

Light violet

[Ni(py)2(ox)]n

NiC12H10N2O4

(46)

304.89

47.20 (47.23)

3.28 (3.30)

9.20 (9.18)

19.3 (19.2)

Light green

[(Ni(pn)(ox)).H2O]n

NiC5H12N2O5

(47) 238.82 25.10

(25.12) 5.10 (5.06)

11.70 (11.72)

24.6 (24.5) Blue

[(Co(en)(ox)).H2O]n

CoC4H10N2O5

(48) 224.93 21.30

(21.33) 4.50 (4.48)

12.40 (12.44)

26.2 (26.1) Brown

[Co(bipy)(ox)]n

CoC12H12N2O4

(49) 303.12 47.52

(47.50) 2.68 (2.66)

9.25 (9.23)

19.5 (19.4) Orange

[(Co(phen)(ox)).H2O]n

CoC14H12N2O6

(50) 363.16 46.28

(46.26) 3.35 (3.33)

7.70 (7.71)

16.3 (16.2) Orange

[Co(py)2(ox)]n

CoC12H10N2O4

(51) 305.13 47.20

(47.19) 3.31 (3.30)

9.20 (9.17)

19.2 (19.3)

Light pink

Chapter 7 328

[Co(pn)(ox)]n

CoC5H10N2O4

(52) 221.06 27.18

(27.14) 4.50 (4.55)

12.70 (12.66)

26.7 (26.6)

Dark pink

[(Cu(en)(ox)).2H2O]n

CuC4H12N2O6

(53) 247.54 19.40

(19.39) 4.85 (4.88)

33.15 (33.12)

25.7 (25.6) Violet

[Cu(bipy)(ox)]n

CuC12H8N2O4

(54) 307.73 46.82

(46.79) 2.65 (2.62)

9.12 (9.09)

20.7 (20.6)

Light blue

[Cu(phen)(ox)]n

CuC14H10N2O5

(55) 349.77 48.06

(48.03) 2.90 (2.88)

8.02 (8.00)

18.2 (18.1)

Light blue

[Cu(py)2(ox)]n

CuC12H10N2O4

(56) 309.74 46.51

(46.49) 3.20 (3.25)

9.05 (9.03)

20.6 (20.5)

Light blue

[Cu(pn)(ox)]n

CuC5H10N2O4

(57) 225.67 26.60

(26.58) 4.50 (4.46)

12.42 (12.40)

28.2 (28.1)

Light blue

7.3.3 IR spectra of Lewis–base adducts of nickel(II) oxalate

As compared to the IR spectrum of nickel(II) oxalate, its

Lewis-base adducts gave several additional and modified peaks.

The νas(CO2) band occurring at 1636 cm-1 in [Ni(H2O)2(ox])n (40)

were found shifted to 1547-1621 cm-1 in its adducts and the

νs(CO2) band observed at 1362 cm-1 was found lowered to

1335-1380 cm-1 in its adducts. The individual details are discussed

below and important frequencies are given in Table 7.6.

In the IR spectrum of the adduct [Ni(en)(ox)]n, 43, the

νas(NH2) and νs(NH2) bands were observed at 3283 and 3158 cm-1

respectively. The bending mode (δNH2) was seen at 1620 cm-1. A sharp

band observed at 1023 cm-1 could be assigned to ν(C-N) stretching of


en. The νas(CO2) and νs(CO2) bands were observed at 1547 and 1335

cm-1 respectively. The νΔ values suggest the bridging character of -

COO- group of oxalate moiety in it.

Table 7.6 IR spectral data of nickel(II) oxalate and its various Lewis-base adducts (cm-1)

Adducts 40 43 44 45 46 47

ν(O-H) 3250 - - 3390 3450

νas(CO2) 1636 1547 1602 1580 1621 1590

νs(CO2) 1362 1335 1352 1345 1363 1380

νΔ 274 212 250 235 258 210

ν(C-O) 1316 1302 1317 1282 1315 1313

C Cν

- - 1633 1646 1605 -

νC N

- 1475 1421 1480 -

ν(C-N) 1023 - - - 1018

ν(C-H) - 771 725 - -

β(C-H) - 1022 - - -

ν(NH2) 3283 3158 - - - 3310 3280

δ(NH2) 1620 - - 1610

(NH2) wag 751 - - 799

M-N stret 526 - - 470

Ring deformation

(outplane)

(inplane)

-

-

498

653

480

639

445

660

-

-

Chapter 7 330

For the adduct [Ni(bipy)(ox)]n, 44, new peaks were observed

at 771, 1022, 1475 and 1633 cm-1 indicating that bipy is

coordinated to Ni through both of its pyridyl nitrogen. The νas(CO2)

and νs(CO2) bands of oxalate moiety were observed at 1602 and

1352 cm-1. The in-plane and out-of-plane ring deformation modes

of bipy were observed to 653 and 499 cm-1 respectively.

The IR spectrum of the complex [(Ni(phen)(ox)).2H2O]n, 45,

gave new peaks at 725,1421 and 1646 cm-1 indicating the presence

of phen. The bands at 1421 and 1646 cm-1 could be assigned to

the ring skeletal vibration of phen. Its ring deformation modes were

observed at 639 and 480 cm-1. The νas(CO2) and νs(CO2) bands of

oxalate group were seen shifted to 1580 and 1345 cm-1 respectively

and the apperance of a broad band at 3390 cm-1 indicates the

presence of lattice water in it.

For the adduct [Ni(py)2(ox)]n, 46, all the characteristic peaks

of pyridine were observed in addition to the peaks due to parent

oxalate. The ring skeletal bands of pyridine were observed at 1605

and 1480 cm-1. The νas(CO2) and νs(CO2) bands of oxalate moiety

were observed at 1621 and 1363 cm-1 respectively. The ring

deformation modes of pyridine were observed at 660 and 445 cm-1 .

The IR spectrum of the adduct [(Ni(pn)(ox)).H2O]n, 47, gave

peaks at 3313 and 3278 cm-1 which are characteristic of νas(NH2)

and νs(NH2) vibrations of coordinated pn. The δ(NH2) band was

observed at 1610 cm-1 and ν(C-N) band was seen at 1018 cm-1. The

νas(CO2) and νs(CO2) bands of oxalate moiety were observed at 1590

and 1380 cm-1 respectively. The appearance of a broad band at

3450 cm-1 indicates the presence of lattice water in it.


As in the case of succinates and malonates we have made

attempts to look at the gradation of νΔ in the nickel(II) oxalate and

its adducts also. While in parent nickel(II) oxalate the νΔ is

274 cm-1, in its adducts the difference is seen to be decreasing

progressively in the order 40 > 46 > 44 > 45 > 43 > 47. This is

consistent with the fact that pn and en are totally σ-donors (with

no π-accepting character) while phen, bipy and py have both σ-

donor and π-accepting nature. The σ-donor ligands would enhance

the electron density on the metal which would in turn make the

metal release more electron to the π* orbitals of the oxalate moiety.

The effect of such back donation would be to decrease the O-C-C-O

bond order in the oxalate which gets reflected in νΔ also. In the

case of phen, bipy and py the Lewis-bases have on their own some

π-acceptor property also and hence will not try to accumulate

much electron density on the metal. Consequently the back

donation to oxalate π* orbital would be less. The trend observed

agrees well with the expectation.

7.3.4 Electronic spectra and magnetic data of Lewis-base adducts of nickel(II) oxalate

The electronic spectra of various adducts of nickel(II) oxalate

isolated were recorded in solid state. Some of the spectra are

reproduced in Fig.7.1. The characteristic special features in the

bands of parent nickel(II) oxalate are seen disappearing and new

set of absorptions are seen emerging in its adducts. The absorption

bands were observed in the region 25910-27620 cm-1, 16260-

18380 cm-1 and 10730-11670 cm-1 in all the adducts. These bands

could be assigned to 3A2g(F) → 3T1g(P) (ν3); 3A2g(F) → 3T1g(F) (ν2) and 3A2g(F) → 3T2g(F) (ν1) respectively in agreement with typical Ni(II)

Chapter 7 332

octahedral complex.(39,40) We have evaluated the ligand-field

parameters Dq, for the various adducts employing the methods as

discussed earlier (Chapter 3). The Dq values among the various

adducts were seen to decrease in the order 43 > 46 > 44 > 45 >

47. The trend is seen to be more or less dependent on the pka

value of the various Lewis-bases. Eventhough the pKa value of pn

is greater than that of en, the Dq value of pn adduct (47) is found

to be less than that of en adduct (43). This may be because of the

relatively less chelating stability of pn as compared to en.

The μeff values evaluated for all the Ni(II) adducts are found

to be in the range 3.01-3.18 BM which are in agreement with the

values expected for octahedral complexes. The electronic

transitions, their assignments and magnetic moment data are given

in Table 7.7.


(a) [Ni(H2O)2(ox)]n, 40

(b) [Ni(en)(ox)]n, 43

(c) [Ni(bipy)(ox)]n, 44

(d) [(Ni(phen)(ox)).2H2O]n, 45

(e) [Ni(py)2(ox)]n, 46

(f) [(Ni(pn)(ox)).H2O]n, 47

Fig. 7.1 Electronic spectra of Lewis-base adducts of nickel(II) oxalate

Chapter 7 334

Table 7.7 Electronic spectral and magnetic moment data of Lewis-base adducts of nickel(II) oxalate

Complex Absor. max ν (cm-1)

Assignments*

Dq (cm-1) β B

(cm-1) ν2/ν1μeff

(BM)

40

25310

15600

10650

ν3

ν2

ν1

1065 0.60 597 1.46 2.92

43

27620

18380

11670

ν3

ν2

ν1

1167 0.65 773 1.57 3.07

44

26110

17850

10950

ν3

ν2

ν1

1095 0.63 741 1.63 3.15

45

25910

17950

10800

ν3

ν2

ν1

1080 0.64 764 1.66 3.18

46

26250

16260

11130

ν3

ν2

ν1

1113 0.61 608 1.47 3.01

47

26040

16610

10730

ν3

ν2

ν1

1073 0.66 697 1.55 3.05

*3A2g(F) → 3T2g(F) (ν1); 3A2g(F) → 3T1g(F) (ν2); 3A2g → 3T1g(P) (ν3)


7.3.5 Interaction of Lewis-bases with polymeric cobalt(II) oxalates

Like nickel(II) oxalate, cobalt(II) oxalate also can be expected to

have an extended polymeric structure as mentioned in section 7.3.1

based on its spectral properties. The set of Lewis-bases chosen for the

adduct formation with the cobalt(II) oxalate were same as those used

for nickel(II) oxalate. Interaction with various Lewis-bases was carried

out in different reaction conditions as before. The details are presented

in Table 7.4. We could not find any indication of depolymerisation

being initiated as none of the Lewis-bases tend to bring the metal

oxalate in solution. The analytical data shown in Table. 7.5 confirm the

1:1 composition (cobalt oxalate : Lewis-base) for all the adducts except

with pyridine. The pyridine adduct, however, has 1:2 composition.

7.3.6 IR spectra of Lewis-base adducts of cobalt(II) oxalate

The presence of Lewis-bases in all the adducts could be

confirmed by their characteristic peaks in the IR spectra. The peaks

due to oxalate moiety were also present with some shift in their

position as compared to the values in the parent metal oxalates. The

asymmetric stretching νas(CO2) band observed at 1635 cm-1 in parent

cobalt(II) oxalate was found shifted to 1600-1622 cm-1 in its adducts.

Similarly the νs(CO2) band observed at 1370 cm-1 was found shifted

to 1350-1388 cm-1 in them. The spectra of individual adducts are

discussed below in detail.

In the IR spectrum of [(Co(en)(ox)).H2O]n, 48, the νas(NH2) and

νs(NH2) band were seen at 3340 and 3204 cm-1 showing the

coordination of en. The νas(CO2) and νs(CO2) bands of the oxalate

group are observed in the adduct at 1600 and 1365 cm-1 respectively.

The δ(NH2) and ν(C-N) bands of en were seen at 1630 and 1061 cm-1

Chapter 7 336

respectively and the appearance of a broad band at 3440 cm-1

indicates the presence of lattice water in it. In the case of

[Co(bipy)(ox)]n adduct, 49, new peaks were observed at 771, 1013,

1455 and 1674 cm-1 indicating that bipy is coordinated to Co through

both of its pyridyl Ns. The C-H out-of-plane skeletal vibration of bipy

(νC-H) at 771 cm-1 gets split into 798 and 737 cm-1 in the adduct

indicating the bidentate nature of 2,2'-bipyridyl. The ring deformation

modes of bipy moiety were seen at 660 and 488 cm-1 in the adduct.

The peaks at 1607 and 1355 cm-1 could be assigned to the

asymmetric and symmetric stretching bands of the –COO- group of

oxalate moiety in the adduct.

The spectrum of [(Co(phen)(ox)).H2O]n, 50, showed new bands

at 730, 1425 and 1640 cm-1 showing the chelating nature of phen.

The νas(CO2) and νs(CO2) bands of the oxalate group were seen at 1605

and 1350 cm-1 respectively. The ring deformation modes of phen

moiety appear at 643 and 428 cm-1 respectively. The presence of

lattice water is confirmed by the appearance of a broad band at 3407

cm-1. In the case of [Co(py)2(ox)]n adduct, 51, new peaks were

observed at 1610 and 1478 cm-1 due to ν(C-C) and ν(C-N) ring

stretching skeletal vibrations of pyridine. The νas(CO2) and νs(CO2)

peaks of oxalate group were seen shifted to 1622 and 1361 cm-1

respectively. The in-plane and out-of-plane ring deformation modes of

pyridine moiety were observed at 632 and 492 cm-1.

In the pn adduct, [Co(pn)(ox)]n, 52, peaks at 3360 and

3240 cm-1 characteristic of NH2 stretching of coordinated pn are seen.

The bands at 1654 and 1048 cm-1 could be assigned as δ(NH2) and

ν(C-N) vibrations of pn. The νas(CO2) and νs(CO2) bands of –COO¯

group of oxalate moiety were observed at 1601 and 1388 cm-1


respectively. All the other important IR absorption frequencies of

cobalt(II) oxalate and its Lewis-base adducts are given in Table 7.9.

The νΔ found for the adducts are in the order

41 > 51 > 50 > 49 > 48 > 52 which is in the expected order when

we consider the σ-donor ability of pn and en and σ-donor and

π-acceptor property of phen, bipy and py.

Table 7.9 IR spectral data of Lewis-base adducts of cobalt(II) oxalate (cm-1)

Adducts 41 48 49 50 51 52

ν(O-H) 3235 3440 - 3407 - -

νas(CO2) 1635 1600 1607 1605 1622 1601

νs(CO2) 1370 1365 1355 1350 1361 1388

νΔ 265 235 252 255 261 213

ν(C-O) 1321 1317 1310 1312 1315 1304

C Cν

- - 1674 1640 1610 -

νC N

- 1455 1425 1478 -

ν(C-N) 1061 - - - 1048

ν(C-H) - 771 730 - -

β(C-H) - 1013 - - -

ν(NH2) 3290 3204 - - - 3310

3240

δ(NH2) 1630 - - 1654

(NH2) wag 778 - - 767

M-N stret 575 - - 551

Ring deformation

(outplane)

(inplane)

-

-

488

660

481

643

492

632

-

-

Chapter 7 338

7.3.7 Electronic spectra and magnetic data of Lewis-base adducts of cobalt(II) oxalate

The electronic spectra of all the adducts of cobalt(II) oxalate

were recorded in solid-state because of their insolubility. Some of

the spectra are reproduced in Fig. 7.2. All the adducts show the

set of bands in the region 15480-15870 and 19530-21550 cm-1.

These are very characteristic of octahedral Co(II) and could be

assigned to 4T1g→4A2g and 4T1g→4T1g(P) transitions respectively.(41,42)

The data are tabulated in Table 7.10.

Table 7.10 Electronic spectral and magnetic data of Lewis-base adducts of cobalt(II) oxalate

Adducts Absor. max ν (cm-1) Assignments

μeff

(BM)

41 18450

14490

4T1g → 4T1g(P)

4T1g → 4A2g

4.57

48 21550

15870

4T1g → 4T1g(P)

4T1g → 4A2g

4.71

49 21010

15580

4T1g → 4T1g(P)

4T1g → 4A2g

4.74

50 21270

15530

4T1g → 4T1g(P)

4T1g → 4A2g

4.77

51 19530

15480

4T1g → 4T1g(P)

4T1g → 4A2g

4.65

52 21320

15600

4T1g → 4T1g(P)

4T1g → 4A2g

4.69


Fig.7.2 . Electronic spectra of cobalt(II) oxalate and its Lewis-base adducts

(a) [Co(H2O)2(ox)]n, 41 (d) [(Co(phen)(ox)).H2O]n, 50

(b) [(Co(en)(ox)).H2O]n, 48 (e) [Co(py)2(ox)]n, 51

(c) [Co(bipy)(ox)]n, 49 (f) [Co(pn)(ox)]n, 52

Chapter 7 340

The room temperature magnetic susceptibility measurements

were carried out and μeff values evaluated for all the adducts. These

were found to be in the range 4.65-4.77 BM. No definite trend in μeff

values could be seen among these adducts. The high spin rather

than low spin state manifested in the μeff values for all the Lewis-base

adducts indicate the weak ligation property of the Lewis-bases with

the parent cobalt(II) oxalate.

7.3.8 Interaction of Lewis-bases with copper(II) oxalate

Just as in the case of nickel(II) and cobalt(II) oxalates, adduct

formation studies were investigated with polymeric copper(II)oxalate

also with the same set of ligands. The interaction was studied in

various reaction conditions and also by changing the stoichiometric

ratio of the parent oxalate and Lewis-bases. These along with some

salient features of the reactions and products isolated are presented

in Table 7.4. The analytical data shown in Table 7.5 confirm the 1:1

composition (metal oxalate: Lewis-base) for all the Lewis-base adducts

isolated except that with pyridine.

7.3.9 IR spectra of Lewis-base adducts of copper(II) oxalate

Like in the case of nickel(II) and cobalt(II) oxalate, copper(II)

oxalate and its Lewis-base adducts also show characteristic peaks in

their infrared spectra. The νas(CO2) observed at 1649 cm-1 in parent

copper(II) oxalate was found shifted to 1580-1624 cm-1 in its adducts

and the νs(CO2) band observed at 1364 cm-1 to 1345-1390 cm-1 in

them. The individual details are discussed below.

In the IR spectrum of [(Cu(en)(ox)).2H2O]n, 53, new bands were

observed at 3306 and 3219 cm-1 which could be assigned as νas(NH2) and

νs(NH2) vibrations respectively. The δ(NH2) band was seen at 1590 cm-1

and the ν(C-N) band was observed at 1044 cm-1. The νas(CO2) and


νs(CO2) bands of –COO¯ group of oxalate moiety were observed at 1596

and 1390 cm-1 respectively. The presence of lattice water is indicated

by the appearance of a broad band at 3390 cm-1.

For the adduct [Cu(bipy)(ox)]n, 54, new bands were observed

at 775, 1019, 1472 and 1661 cm-1 indicating that bipy is coordinated

to Cu through both of its pyridyl N. The C-H out-of plane skeletal

vibration of bipy (νC-H) at 775 cm-1 gets split into 782 and 731 cm-1 in

the adduct. This reflects the bidentate nature of 2,2'-bipyridyl.

Moreover νas(CO2) and νs(CO2) bands of oxalate moiety were seen

shifted to 1597 and 1360 cm-1. The ring deformation modes of bipy

appear at 662 and 486 cm-1 respectively.

In the IR spectrum of [Cu(phen)(ox)]n, 55, new peaks were seen

at 723, 1427 and 1663 cm-1 showing that phen is coordinated through

both of its pyridyl N. The νas(CO2) and νs(CO2) bands of oxalate moiety

were observed at 1603 and 1345 cm-1. The ring deformation modes of

phen moiety appear at 646 and 482 cm-1 respectively.

For the adduct [Cu(py)2(ox)]n, 56, new bands are seen at 1600

and 1487 cm-1 which could be assigned to ν(C-C) and ν(C-N) ring

stretching skeletal bands of pyridine. The peaks at 1624 and 1362

cm-1 are due to νas(CO2) and νs(CO2) modes of –COO¯ group of oxalate

moiety. The ring deformation modes of pyridine moiety were observed

at 687 and 443 cm-1 respectively.

In the IR spectrum of the adduct [Cu(pn)(ox)]n, 57, the νas(NH2)

and νs(NH2) vibrations of coordinated pn were observed at 3290 and

3250 cm-1. The νas(CO2) and νs(CO2) bands of oxalate moiety were

observed at 1580 and 1378 cm-1 respectively. All other relevant IR

Chapter 7 342

absorption frequencies of copper(II) oxalate and its Lewis-base

adducts are shown in Table 7.11.

In the system also we have monitored the trend in νΔ among

the various adducts. The order was found to be 42 > 56 > 55 > 54 >

53 > 57.

Table 7.11 IR spectral data of Lewis-base adducts of copper(II) oxalate (cm-1)

Adducts 42 53 54 55 56 57

ν(O-H) - 3390 - - - -

νas(CO2) 1649 1596 1597 1603 1624 1580

νs(CO2) 1364 1390 1360 1345 1362 1378

νΔ 285 206 237 258 262 202

ν(C-O) 1319 1310 1294 1298 1316 1269

C Cν

- - 1661 1663 1600 -

νC N

- 1472 1427 1487 -

ν(C-N) - 1044 - - - 1038

ν(C-H) - 775 723 - -

β(C-H) - 1019 - - -

ν(NH2) 3306

3219 - - -

3290

3250

δ(NH2) 1590 - - 1626

(NH2) wag 714 - - 785

(M-N)stret 525 - - 498

Ring deformation

(outplane)

(inplane)

-

-

486

662

482

646

443

686

-

-


7.3.10 Electronic spectra and magnetic data of Lewis-base

adducts of copper(II) oxalate

The electronic spectra of various adducts of copper(II)

oxalate were recorded in solid state. Some of these are reproduced

in Fig.7.3. The data are presented in Table 7.12. The authenticity

of all the peaks was confirmed by recording the spectrum by

repeated sample preparation.

In all the adducts generated in the present study a broad

band occur in the region 14180-18650 cm-1. This is indicative of

tetragonal configuration around copper(II) ion.(46,47) Moreover both

n→π* and π→π* bands were found to be blue shifted and appearing

in the region 3330-33670 cm-1 and 40160-41150 cm-1 respectively,

compared to that of the parent complex. Further, the electronic

spectra of all the complexes exhibit an intense absorption band in

the region 26450-28980 cm-1 which could be assigned due to

charge transfer transitions.

Chapter 7 344

Table 7.12 Electronic spectral data and magnetic moments of Lewis-base adducts of copper(II) oxalate

Adducts Absorption max

ν (cm-1) Assignments

μeff

(BM)

42

40000 33220 26040 13850

π→π*

n→π*

Charge Transfer 2B1g → 2A1g

1.43

53

40160 33330 28980 18650

π→π*

n→π*


1.62

54

40480 33670 28090 14490

π→π*

n→π*


1.67

55

41150 33440 27700 14180

π→π*

n→π*


1.68

56

40320 33550 26450 15190

π→π*

n→π*


1.57

57

40810 33330 28190 15870

π→π*

n→π*


1.59


(a) [Cu(ox)]n, 42

(b) [(Cu(en)(ox)).2H2O]n, 53

(c) [Cu(bipy)(ox)]n, 54

(d) [Cu(phen)(ox)]n, 55

(e) [Cu(py)2(ox)]n, 56

(f) [Cu(pn)(ox)]n, 57

Fig.7.3 Electronic spectra of Lewis-base adducts of copper(II) oxalate.

The magnetic moment values of the present copper(II)

complexes vary in the range 1.57-1.68 BM (Table 7.12). The

comparatively lower magnetic moment values seen for all these

polymeric adducts indicates the possibility of structures with close

Cu-Cu proximity.(48)

Chapter 7 346

7.3.11 EPR spectra of Lewis-base adducts of copper(II) oxalate

Compared to the adducts of copper(II) succinate and

copper(II) malonate, the adducts of copper(II) oxalate are

insoluble in most of the solvents. Their polymeric nature is also

evident from the electronic and IR spectral data. Owing to this, the

EPR spectra of this compounds could be recorded in solid state

only at room temperature. Fig 7.4 gives the spectra of en adduct

53, bipy adduct 54, py adduct 56 and pn adduct 57. Eventhough

the spectra were not well resolved, their features appear almost the

same in all the cases. Comparing with some of the known spectra,

the g⎜⎜ and g⊥ values for this adducts could be evaluated. These are

given in Table 7.13. The trend g⎜⎜>g⊥>2.0023 seen in all the adducts

indicate dx2-y2 ground state in them.(49) The parameters giso and G

could be calculated for the adducts by using the equations

mentioned earlier. The axial symmetry parameter, G, which

indicate the nature of exchange interaction between the copper

centres for the adducts has value below 4.(50) Significant exchange

interaction can therefore be expected from all these adducts. The

nature of the EPR spectra of the pn adduct 57 and its G value

(1.60) indicate that the structural features of 57 could be much

different from those of others.


(a) [(Cu(en)(ox)).2H2O]n, 53

(b) [Cu(bipy)(ox)]n, 54

(c) [Cu(py)2(ox)]n, 56

(d) [Cu(pn)(ox)]n, 57

Fig. 7.5 The EPR spectra of the polymeric adducts of copper(II) oxalate.

Table 7.13 The various EPR parameters of the polymeric adducts of copper(II) oxalate

Adducts g⎜⎜ g⊥ giso G

53 2.18 2.06 2.10 3.00

54 2.21 2.08 2.12 2.63

56 2.16 2.07 2.10 2.29

57 2.14 2.09 2.11 1.60

Chapter 7 348

All the analytical, spectral (IR, electronic, EPR), and

magnetic moment data of the adducts of metal(II) oxalate clearly

indicate that all of them have a polymeric octahedral structure with

bis-bidentate chelating oxalate functions. The high insoluble nature

of all the adducts in various organic solvents also gave a clear

evidence for their polymeric structure.

References

1. (a) C. Sterling, Nature; 205 (1965) 588

(b) C. Sterling, Science; 146 (1964) 518

(c) O. C. Pluchery, J. C. Mutin, J. Bouillot and J. C. Niepce, Acta Crystallogr; C45 (1989) 1699

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