CHAPTER I

INTRODUCTION AND SCOPE OF THE PRESENT INVESTIGATION

The multipronged research carried out in the field of coordination

chemistry has played an important role in the fast development of

inorganic chemistry. In fact, this flourishing development of inorganic

chemistry in general, and coordination chemistry in particular, is only

about five decades old. Despite the great progress from the times of

Jorgensen and Werner in the field of coordination chemistry, the 'heart

of inorganic chemistry', the real milestone was Bjerrum' s dissertation

published in 19411 . In recent years the field of coordination chemistry

has received a large amount of experimental work and this has, no doubt,

been supplemented by the extensive application of ligand field and

molecular orbital theories. These developments in the field of coordination

chemistry have led to a good interpretation of the nature of chemical

bond , structure and reactivity of coordination com pounds. The advent

of sophisticated physicochemical tools has made this awesome development

essentially at an exponential rate.

The actinide series

The actinide series comprises the 14 elements following actinium

and ending with lawrencium, the 103 rd element in the Periodic Table.

All the known isotopes of these elements are radioactive and therefore,

of the grea_test importance in the study of nuclear chemistry. Studies

2

on properties of the actinides and their compounds are somewhat difficult

because only thorium and uranium occur naturally in quantities that permit

work on macrochemical levels, while the other elements are made

artificially and the quantities obtainable are such that microchemical

methods must be used.

In early days there was controversy regarding the electronic

structures of these elements. Th, Pa and U show certain resemblances

with !VB, VB and VIB transition metals, respectively. Furthermore, the

increase in the number of oxidation states exhibited by Ac, Th, Pa and

U and the increased stability of the higher oxidation states are reminiscent

of a transition series. But with the production of neptunium, plutonium

and other transuranium 2 3

elements it was made necessary to think of

a different classification as the 'actinide series' sim"ilar to the lanthanide

series. From neptunium onwards the lower oxidation states become more

and more stable and finally the oxidation state profile collapses into

a lanthanide type pattern to the heavier members. Nevertheless, we

should not lose sight of the fact that in the earlier actinides, the 5f

electrons contribute to covalent bond formation and these elements do show

certain similar! ties with the transl tion metals.

As a consequence of poor shielding of the 4f and 5f electrons

there is a steady increase in the effective nuclear charge and concomitant

reduction in size. However, there is a major difference between the

lanthanide and actinide series - although the actinide contraction initially

parallels that of the lanthanides, the elements from curium are smaller

3

than that might have been expected, probably resulting from poorer

shielding by the 5f electrons in these elements.

Coordination chemistry of the actinides

The actinide ions behave as 'hard acids' according to Pearson

and bond preferentially to fluorine, oxygen and nitrogen donor ligands 4•

A variety of oxidation states pertain especially to the first half of the

actinide series, where there is a situation in which the 5f, 6d, 7s and

7p orbitals having comparable energy can be involved in bonding. This

situation is indicated by the fact that the actinides are much more prone

to complex formation than the lanthanides. This is because less energy

is required to convert 5f electrons to 6d electrons for the actinides than

to convert 4f electrons to 5d electrons for the lanthanides5. As a result

of this covalent-hybrid bonding involving 5f electrons, actinides can form

complexes with certain TI bonding as well as anionic ligands. The general

tendency of complex formation, which is governed

ionic size and charge, is in the order M4+ > MO�+

by factors such as

> M3+ > MO+ for the2 actinides. The complexing ability of the anions is in the order F- > No;>

CC > Cl0-4

for uninegati ve ions, and in the order co2- > C o2- > so2- for 3 2 4 4

dinegati ve ions.

The absence of extensive interaction of ligand with 5f orbitals

mitigates ligand field stabilization effects ( LFSE), which reduces the

overall stability of the actinide complexes and this also provides high

coordination numbers and novel geometries to the actinides, which are

4

uncommon in transition metal complexes. Moreover, ·actinide complexes

are labile in solution. The differences between the transition and inner-6 transition metal complexes have been summarized by Karracker .

The actinide complexes render a large number of electronic

transitions in the near UV, visible and IR regions. 3+ Am and heavier

actinide · ions have sharp line-like spectra, resembling that of the

lanthanides, while in Pu3 + and lighter actinide ions the absorption peaks

are broadened as in the case of the transition series due to greater

'exposure' of 5f orbitals and consequently enhanced ligand-metal

' t t' 7 1n erac ions . The electronic transitions occurring between 5f orbitals

and the orbitals of the coordinated ligands are strongly affected by the

nature of the ligands. Generally they are quite intense and the bright

colours of many actinide complexes are ascribed to charge transfer bands8.

The decade 1960-70 saw a world-wide interest in the compounds

of the actinides. Comyns' review on the actinide complexes speaks of

the status of coordination chemistry of the actinides in 19609. Later

a number of good reviews on various aspects of the coordination chemistry

of the actinides have been publishect 8 • 1°-16. However, none of them

gives a complc::te picture of the work done so far in this field.

Uranium

Klaproth discovered uranium as early as 14f9 and he named it

after the planet Uranus. Uranium occurs in a few trace minerals in the

combined state. Its proportion in the earth's crust is O. 000003 %, but

5

it is more abundant than silver, cadmium, mercury and iodine. The

principal 'stockists' of uranium are the U.S.A. , Canada, South Africa

and Australia. Deposits in India have been reported from West Bengal,

Andhra Pradesh and Central India.

Uranium has the highest atomic weight among any naturally

· 1 h 11 · · f · 238

u occurring e ements. T e natura y occurring isotopes o uranium are

(99.25%). 235

u (0.7%) and 234

u (0. 05%). and have halflives of 4.5x109

,

7x108

and 1. 6x105

years, respectively. All the three isotopes are

a-emitters. The isotope234

u is fissile and the discovery of uranium

fission in 1939 had stimulated a very detailed study on uranium chemistry,

which led to the discovery of transuranium elements. Uranium is of great

commercial importance as a nuclear fuel. It is a lustrous white metal

which rapidly gets oxidized at temperature above 200° C.

Oxidation states of uranium

Uranium exhibits four well-defined oxidation states, viz., +3,

+4, +5 and +6. Of these, the tetra and hexa positive states are more

important. The u3+

ion is unstable and can be oxidized even by air.

Solutions containing intense red U 3+ ions are unstable and are oxidized

rather rapidly by water with the formation of the u4+

ions. The u3+

ion is also hydrolyzed by water.

solid as trifluoride and trichloride.

17-20species have been reported .

However, the +3 state is stable in

3+ Only a very few complexes of U

6

4+ Solutions of the U ions have a characteristic green colour and

are more stable towards oxidation than those of the tripositive species.

However, 4+ ·

2+ - ,. U ion is oxidized by oxygen to uo

2 , the uranyl ion. The

4+ U ion is much more susceptible to hydrolysis than the +3 state. That is, ,

....

+

u4+ ion can form complexes with anionic ligands such as HSO�, No; and

Cl . A large number of solid uranium (IV) complexes, .with varying types21-25of ligands have been reported

The uo; ion is extremely unstable, tending to disproportionate

rapidly into u4+ and UO�+ species except in the pH range 2 to 4, where

the disproportionation is slow.

2UO+ + 4H+

2 +

+

Pentavalent uranium exists in the solid state in the pentahalides; The

available literature on the coordination chemistry of uranium(V) is

meagre26-29 in comparison with the voluminous data available for the

other oxidation states.

The most stable oxidation state of uranium is the + 6, the principal

chemistry of which is that of the dioxo ion, UO�+ Solutions of UO�+

(uranyl or dioxouranium (VI)) ions are yellow in colour and distinctly

acidic as a result of hydrolysis. Hydrolysis leads to the production 2+ 2+ of various polymolecular complex species, such as u

2o5 , u

3o8 , u

3o8(0H)

7

The most extensively explored complexes of uranium 2+ are those of uo2 ion and a rather exhaustive literature survey on them

is also given in this chapter.

Uranyl ion

The metal oxocation complexes form an important fraction of recent

coordination chemistry. The existence of a strong multiple metal-oxygen

covalent bond capable of persisting in various chemical environments is,

in itself, of theoretical as well as experimental significance. The

importance of oxocations arouses the curiosity about using some of the

properties of the metal-oxygen multiple bond, as these properties can

well be employed to investigate the· nature of other metal-ligand bonds30.

One of the most thoroughly investigated, the best characterized and the

most stable oxocations is uranyl ion31 In crystalline compounds as well

as in solutions the UO�+ ion is evidently linear. For MO�+ ions, both

the bond strength and chemical stability towards reduction decrease in

the order U > Np > Pu > Am. The molecular orbital structure allows detailed

interpretation of spectroscopic and magnetic data of uo� + ion32

The common uranyl salts are the nitrate hydrates, carbonate,

oxalate trihydrate, sulphate hydrates, acetate dihydrate and halides.

The most important one is the nitrate which crystallizes with six, three

or two molecules of water. The most unusual and significant property

of uranyl nitrate is its solubility in numerous ethers, alcohols, ketones

and esters.

8

Stereochemistry and coordination numbers of uranyl ion

The coordination polyhedra of actinide ions having higher

coordination numbers - seven' through twelve - haye been extensively and

sufficiently investigated with the advent of automated X-ray methods,

while ambiguities remain in solution where complicated system takes

33 place . There are actinide complexes with coordination numbers of ten

or higher as these elements have sufficient number of valence shell

orbitals. Ligand field interactions are at best minimal in 5f inner-

transition element chemistry. Consequently, the complexes formed by_

these elements can be considered kinetically as labile, and they will

have appreciable flexibility in the coordination geometries they adopt.

Thus, in the actinides the steric crowding about the central atom becomes

the most

34 topology

important factor in determining the stereochemistry and

Obviously the type of polyhedron obtainable for an actinide

ion depends upon the nature of both the central metal ion and the ligands.

The charge-to-radius ratio of the central metal ion must be one that

maximizes the metal-ligand attraction and minimizes the ligand-ligand

repulsion. The attraction of the metal ion towards the ligand, if the

former is relatively highly charged, will be sufficient to overcome the

repulsion between the ligands.

Although the common coordination numbers exhibited by the uranyl

ion are seven and eight, other coordination numbers of six, nine, ten

and twelve are not rare. For a seven coordinate uranyl complex a

pentagonal bipyramidal geometry is the most favourable, which only allows

9

the trans O=U=O group to be linear. Most of the uranyl complexes have

mononuclear pentagonal bipyramidal geometry, but polynuclear configurations

are also found. Pentagonal bi pyramidal geometry has been reported for

[U02

F5

]3- ion in the crystal lattice of the potassium salt on the basis

of a two-dimensional X-ray analysis35 The central uranium atom has

a coordination number of seven in

The two uranyl oxygens, in these urea complexes

occupy the apical positions of the pentagonal bipyramid polygon of the

heptacoordinated uranium atom.

The hexagonal bipyramid is the polyhedron characteristic of

octacoordinate uranyl complexes, the apical positions being occupied by

the two uranyl oxygens. X-ray and neutron diffraction studies have

demonstrated that the configuration around the uranium atom is an irregular

hexagonal bi pyramid in Rb [ uo2

( N03

) 3

] 38 The structures of

[U02

(N03

lz

(Hz

O)z

].4Hz

O, [U02

(N03

)2

(H20)�.H

20 and [U0

2(N0

3l

z(H

zOl

zl

have been proposed as a · result of two-dimensional X-ray studies. The

linear uranyl group is equatorially surrounded by an irregular hexagon

of six oxygen atoms, two from two equivalent water molecules and four

f t b. d t t . t t 39-41 ram wo 1 en a e m ra e groups Uranyl icm is surrounded by a

hexagonal coordination sphere of oxygen atoms

plane which is normal to the linear uo� +

bonded in the equatorial

group in [ uo2 ( tetrahydro-

and ruo2

(ethyl carbamate) ( N03

) 2

J crystals 42 • 43. X-ray

and molecular structural studies of uranyl nitrate complexes with phosphine

and arsine oxides also indicate eight coordinated uranium atom 44 • 45.

Very recently, a number of Schiff base complexes of uranyl ion

having coordination numbers six, seven, eight, nine and twelve for the

10

. 46-48central uranium atom have been synthesized and characterized . X-ray

structural investigations have shown that the central uranium atom is six

coordinated in the uranyl-sugar complexes containing D-glucuronate and

. 49 50 fructose moieties ' . Uranium has been reported to be nine coordinated

in the complex [Co(en)3](NH4)[uo2(NCS)5(N03)J and its guanidinium analogue

1151, 52 as we .

A brief review on uranyl complexes

Among the complexes of uranium, those of the uranyl ion represent

the most extensively studied ones. A brief review is presented on the

uranyl complexes under the following headings based on the donor atoms.

Complexes of oxygen donor ligands

Numerous uranyl complexes with S-diketones and related dicarbonyl

53-56 compounds have been prepared Sacconi and Giannoni have recorded

and discussed the electronic and IR spectra of a number of uranyl

complexes of . 57-59 S-d1ketones . There have been numerous reports on

the preparation and characterization of uranyl-thenoyltrifluoroaceto'ne

60-62complexes Highly stable uranyl complexes of tropolone ( 2-hydroxy-

2,4,6- cycloheptatrien-1-one) have been synthesized and a complete X-ray

· t' t ' f th h b carri'ed out

63 -66

. B' 1 1 inves iga 10n o ese as een inuc ear comp exes

of uranyl ion with tetraketones such as 1,1'-(1,3-phenylene)bis-1,3-butane-

dione and 1,1'-(1,4-phenylene)bis-1,3-butanedione have been isolated and

characterized by various physicochemical methods67

.

11

Uranyl complexes with acid oxygen donors such as uranyl tartrate

and uranyl citrate have been isolated and characterized68

. Crystallo-

graphic data are available for the dihydrate and trihydrate of uranyl

. 69 70 sallcylate ' In addition to these, Muller has prepared and analysed

many uranyl derivatives of substituted carboxylic acids and 71

phenols .

Uranyl carboxylates having the general formula uo2

L2

. H2

o ( where HL =

formic, acetic or prop ionic acids, chloro acids or oxalic acid) and also

some mixed uranyl carboxylates have been 72

prepared All these

complexes have been characterized by thermal decomposition studies.

Recently, uranyl complexes containing fluoride and malonate have been

synthesized and characterized 73

. Some polymeric uranyl pyrazine-2, 3-

dicarboxylate complexes such as = pyrazine-2, 3-

dicarboxylic acid; L' = 2-methylpyridine-1-oxide, n = _1,3; L' = dimethyl-

sulphoxide, hexamethylphosphoramide, n = 2; L' = H2o, n = 2-4) have

been isolated and characterized 74

.

with pyridine carboxylic acids 75

Robel has reported uranyl complexes

been prepared and characterized 76

. The solubilities of the ternary

systems, uranyl ni trate-isopropyl ether-water and uranyl ni trate-n-propyl

ether-water have been measured and solid complexes have been isolated 77•

The tetrahydrofuran complex, uo2

(THF)2

(N03

)2

, has been prepared and

its crystal structure has been determined 78

. The chelating ability of

crown ethers with respect to uranyl ion has been studied. 18-Crown-6

complexes of uranyl nitrate, having different water of hydration, have

been prepared and . 79 80

characterized ' But alternative syntheses and

12

molecular structures of these. complexes have also been reported Bl-BJ.

Complexes such as uo2

(dicyclohexyl-18-crown-6)(N03

)2

. 2tt2o and uo2

(15-

crown-5) ( N03

) 2

have been prepared and characterized BO. Uranyl fluoride

complexes with all the above macrocyclic poly�thers have also been

prepared and characterized84

. The synthesis and characterization of the

uranyl nitrate complexes with cyclic polyethers such as dibenzo-18-crown-6

85 and benzo-15-crown-5 have been reported . The crystal structure of

uranyl nitrate dihydrate -1, 4, 7, 10-tetraoxacyclododecane has been reported86

.

Uranyl nitrate and chloride complexes of crown ethers such as dibenzo-18-

crown-6, benzo-15-crown-5 and 18-crown-6 having different chemical

compositions from those reported in the literature have also been

synthesized and characterized87

•88

. Uranyl complex of 2 , 4-diketo-16-

crown-5 has been prepared and investigated by chemical analysis, IR

spectral analysis, thermogravimetry, differential thermal analysis and

X-ray analysis89

.

Solid state interaction between urea and uranyl nitrate hexahydrate

or uranyl nitrate diurea, results in the formation of a series of complexe3

with metal to urea ratios 1: 2, 1: 3, 1: 4 and 1: 5 and these complexes have

been characterized by IR spectral and neutron diffraction studies36 ' 9o. 91.

Uranyl nitrate complexes with substituted ureas such as N, N, N', NL

tetramethyl urea, cyclic propylene urea 2 ( 1H )-tetrahydropyrimidinone and

· cyclic ethylene urea 2-imidazolidinone have been prepared and characterized

by different physicochemical methods92

. Thermosynthesis and thermal

decomposition of uranyl nitrate-urea complexes have been carried out by

Seml·nara et al 93

•94

V tl th 1 't t H ery recen y, ree new urany n1 ra e-urea-2o

13

complexes have been isolated and characterized by X-ray diffraction

studies95. The interaction of uranyl phosphate with some substituted

ureas produces a series of complexes96. Complexes of the general formula

= dodecahydro-closo-dodeca-

borate; L = urea, n = 3, 5, 6, 7, 8) have been synthesized and characterized 97•

Kuznetsov et al have reported the preparation and crystal structure of

tetrakis ( tetramethylurea) dioxouranium (VI) dodecahydrododeca borate 98.

Oxygen donor amine N-oxide complexes of uranyl nitrate such

as uo2(Me3No)2(N03)2 and uo2(Me3No)4

(N03)2 have been isolated99. The

above two amine N-oxide complexes have eight coor:dinated central uranium

atom with a hexagon of six oxygen atoms bonded in the equatorial plane

which is normal to the linear uo�+ group.

Uranyl nitrate complexes of neutral organophosphorus compounds

are usually studied in solution and several such complexes have been 100-102 reported . A range of uranyl complexes of the type uo2L2(N03)2

( where L = phenacyldimethylphosphine oxide, methyldiphenylphosphate,

triphenylphosphine or arsine oxide and trimethyl or triethylphosphine

oxide) have been synthesized and their crystal and molecular structures

have been established45 • 1°3-107. In all these complexes uranium atom

is eight coordinated and the uranyl ion is surrounded equatorially by

an irregular hexagon of six oxygen atoms. Hexamethylphosphoramide (HMPA)

forms a complex of the type uo2(HMPA)2(N03)2 with uranyl nitrate9i, 108.

Recently, 1-hydroxyethylene-1, 1-diphosphonic acid and ni tromethylphos­

phonic acid complexes of uranyl ion have been prepared109 , Both these

14

ligands are coordinated to the uranium atom through the phosphonate

groups. Frangulyan et al have reported the thermol¥.tic studies of uranyl

hydroxyethylidenediphosphonate110 . Cocarboxylase chelates of uranyl

ion have been isolated in the solid state and the IR and PMR studies

suggest that the pyrophosphate groups are coordinated to the uranium 111 atom .

Sulphoxide complexes of uranyl ion such as uo2

(Me2so)

2(N03)

2,

uo2

(Ph2so)

2(N03)2 and uo

2cn-Bu

2so)

2(N03)

2 (where Me

2so = dimethyl­

sulphoxide, Ph2so = diphenylsulphoxide, _!!-Bu2so = di-n-butylsulphoxide)

have been synthesized and characterized112-114. From IR spectral studies

the sulphoxides appear to be coordinated through the oxygen of the S-0

groups. Very recently, uranyl chloride and uranyl nitrate complexes of

sulphoxides such as Me2so and Et2so ( diethylsulphoxide) have been

115 reported . Polymeric uranyl complexes of formaldehyde-£-hydroxybenzoic

acid-urea copolymer and salicylic acid-thiourea-trioxane copolymer have

been prepared and characterized 116 • 117. Copolymers and their polychelates

are antifungal and antibacterial agents. Recently, uo2

.,.sugar complexes

have been synthesized and characterized by X-ray crystallographic studies49 • 5�

�lex.es of nitrogen donor ligands

Uranyl complexes with pure nitrogen donors such as pyridine,

a -picoline, a -benzylpyridine and 1, 10-phenanthroline have been . 118-120 synthesized and characterized . Seminara et al have synthesized

and characterized uranyl complexes of 1, 2-dipyridylethylene isomers121 • 122

Some polymeric complexes of hydrazine and substituted hydrazines having

15

the general composition, uo2

L4x2

(where L = N2

H4, PhNHNH2

or Me2NNH

2:

123 X = Cl, Br, I, No3 or NCS) have been reported .

Uranyl nitrate 124been reported

complexes with triethylamine and ammonia have

also Uranyl chloride complexes of triethylamine in

acetone such as Et3NH[u2

o5

ci3(Me2

co)(Et3N)J. Et3NH[u2

o5

c13(Et3N)3J and

Et3NH[U308c13(Me2

co)Et3N)J have been prepared and characterized by

X-ray diffraction method125. Mixed ligand complexes of some simple

and heterocyclic amines having the general composition

(where = lactic acid; L' = ethylenediamine, dimethylaniline,

diethylamine, 2_-phenylenediamine, pyridine or a -picoline) have been

reported126. Mixed ligand complexes of uranyl ion also with organic anions

and diaminodiphenylene have been synthesized and characterized127.

Complex of 1-( 2 ' -hydroxybenzyl)-2-( 2 ' -hydroxyphenyl )benzimidazole with

UO� + ion has been synthesized and its IR spectral studies suggest that

the ligand is unidentately coordinated to the metal ion through the tertiary

ni trogen128 .

Complexes of nitrogen and oxygen donor ligands

The coordination power of 8-hydroxyquinoline is well-known for

uranyl ion. 8-Hydroxyquinoline has been used for the determination of

uranium by gravimetric, volumetric and colorimetric methods. It forms

the mode of complexation has been extensively studied129 • 130. Three

molecules of 8-hydroxyquinoline are in the plane perpendicular to the

O=U=O group. The neutral molecule is unidentate through the oxygen atom

16

while the other two molecules are bidentate N-0 donors.

c9H7No. CHC13

obtained by crystallization from chloroform has been

well-established through X-ray structural determination 131, 132 5, 7-Dihalo-

8-hydroxyquinolines form complexes with uranyl ion, but it is difficult

to assign their correct composition 133 The sodium salt of 5-ni troso-6-

hydroxyquinoline forms a comp�ex with uranyl ion134. Polymeric uranyl

complexes with poly ( 8-hydroxy-5, 7-quinolinylenecarbonyl vinylene) and

poly( 7-acetyl-8-hydroxyquinoline-5-aldehyde) have been isolated 135' 136.

Uranyl salts give precipitates of double uranyl cupferrates

MU02(c6H5N2o2)3

(where M = Na, K, Rb,

1 t. 137' 138 U 1 1 . th N 0 so u 10ns . rany comp exes w1 -

have been synthesized and characterized 139-142

Cs or NH4

) in neutral

bidentate amine N-oxides

( N-alkylhydroxylamino )-

biS::::.( oxalate) dioxouranate complex having a hexagonal bi pyramidal geometry

143 has been reported N-benzoyl-Q-tolylhydroxylamine forms stable

complexes with uranyl ion and this reagent has been used for the

144 gravimetric determination of uranium by direct weighing of the complex

Uranyl hydrazine carboxylate derivative with the formula

The N-0

donor ligand 4', 5 '-bis( salicylideneamino) benzo { 15-crown-5} forms a complex

with uranyl ion146 Uranyl complexes of cytosin and cytidine phosphates

have been investigated by spectrophotometric and conductometric studies147.

Two new formazans, viz., 1-phenyl-5-{2'-carboxyphenyl)-3-(3'-methyl-2'-

quninoxalyl )formazan and 1-phenyl-5-( 2' -carboxyphenyl)-3-( 3 '-methyl-2 ' -

quinolyl)formazan form well-defined 1 :2 complexes with uranyl ion148

Uranyl polychelates of poly(Q-N-acryloylaminobenzoic acid) and poly(m-N-

17

acryloylaminobenzoic 149 150

acid) having octahedral geometry have been·

reported ' These polychelates are intensely coloured and insoluble

in all common sol vents.

Complexes of sulphur donor ligands

The formation of a coordinate bond between uranyl ion and

typically 'soft' sulphur atom is improbable because the uranyl ion is

a 'hard acid' according to 4 Pearson . But when sulphur is in an

appropriate position in a chelating ligand it can be bonded to uranyl

ion.

Uranyl dithiocarbamate had first been mentioned by Delepine,

but were not characterizect151. Later, Malatesta has prepared a number

of complexes of the general formula uo2(R2dtc)2 (where R = ethyl, methyl,

piperidine, pyrrol, etc., dtc = dithiocarbamate)152. Some colorimetric

applications have also been made of uranyl dithiocarbamates which give

brightly coloured solutions153• 154. A series of complexes of the type

U02(R2dtc)2L (where L = neutral unidentate ligands such as Ph3Po, Ph3As0

or Me3Po) have been prepared and their crystal structures have been

reported 155 • 156. Uranyl complexes with sixteen membered ring molecules

containing phosphorus and sulphur have been synthesized and identified157.

Uranyl complexes of some sulphur donor ligands such as N, N, N', N'-tetra-

methylthiourea, N, N-dimethylthiourea, methylthiourea, ethyl thiourea,

pyridine-2-thiol and 4, 6-dimethylpyridine-2-thiol have also been. isolated

and characterized by IR and Raman spectrometry158.

phenylthiosemicarbazone) complex of UO� + ion has , been

Acetylacetonebis(4-

isolated and

18

characterized159

. Sulphur donor Schiff bases derived from salicylaldehyde

and substituted salicylaldehydes and 3-aminothiophenol form solid complexes

with uranyl ion 48

Potassium hydroxyethylxantha te ( L' ) and potassium

ethylenedixanthate { L") form octahedral complexes of the type uo2

L' and

uo2L 11 with uranyl salts

160.

Anionic complexes

A variety of uranyl fluoro complexes have been identified in the

MIF-uo

2F

2-H

2o syst,3m {where M

I = K or Rb)

161-164. Hydrated complexes

II II · of the type M uo

2F

4.4H

2o {where M = Mn, Co, Ni, Cu, Zn or Cd) have

been crystallized from aqueous solutions165

.

reported to be cubic, the O and F atoms being arranged as a slightly

distorted pentagonal b' 'd

166 1pyram1

formation of complexes of the

I {where M

I Na M Cl. 3Uo

2c1

2= or

Vorebei et.al have reported the

types I

M2uo

2c1

4,

I M Cl. 2Uo

2c1

2and

K)167

0 A series of nonstoichiometric

complexes MIU0

2Cl {where M

I = K, Rb or Cs, X = - 0.8) have · been

X X

prepared and their X-ray diffraction studies have been carried out168

.

The tri-N-thiocyanatocomplexes, MI

[U02{NCS)

3{tt

2o)

2] {where M

I

= Na, K or NH4

) which behave as 1 : 1 electrolytes in methanol have been

prepared and ch3racterized169

. The [U02{NCS)

5]

3- anion in caesium salt

has a pentagonal bipyramidal geometry With the five NCS groups in the

equatorial 170

plane

thiocyanate and acetate

and

The rather unusual

have been

caesium ammonium com pound,

Complex anions, with

-172reported The IR data

19

of these complexes show that all the NCS groups appear to be terminal. 3-The anionic oxalato-N-thiocyanato complex [U02(NCS)(C2o4)2] has been

173 reported

Solid uranyl complexes of the type MI[uo2(N03

)3

] (where MI =

K, NH4

, Rb, Cs, NEt4

, NH2

Et2

or NMe4

) and M�[U02

(N03

)4

] (where MI

174-179 = NH4, NH3

Et , Rb or Cs) are known . Uranyl acetate in presence

of excess of sodium acetate in dilute acetic acid gives a crystalline

precipitate of Na[uo2(cH3

coo)3

J. the carboxylate groups are bidentate

and equivalent180 Anionic sulphato complexes of uranyl ion in nonaqueous

solutions having the formula (R4

N)2

[uo2

cso4

)2

J have been prepared and

h t . d181 c arac er1ze •

Complexes of Schiff base ligands

Because of their elegantly simple technique of synthesis and

versatility as coordinating agents, Schiff bases have been extensively

used as ligands. Schiff bases have the general structure R-N=C-R', where

R and R' are alkyl, cycloalkyl, aryl or heterocyclic groups which · may

be variously substituted. Schiff base-metal chelates are widely studied

as they are found to act as model systems of biological interest182-186.

The coordination compounds of Schiff bases have stimulated work in 187-191 magnetochemistry and spectroscopy . Schiff bases have been reported

192-195 . 196-199 200 203 to have antimicrobial , anticancerous , bacteriostatic - ,

f . t t· 204-209 d t b l t t· 210-212 t· ·t· ung1s a 1c an u ercu os a 1c ac 1 v1 1es. These properties

of Schiff bases are considerably enhanced by the presence of metal

. 213-21410ns

20

Metal derivatives of Schiff bases are known as early as 1840215 •

Both synthesis and properties of Schiff base complexes are very often

related to the associated metal and those aspects have been discussed

in detail by Lindoy and Layer216' 217. Various aspects of their chelating

characteristics are discussed by Dewar and Mellor and Saul Patai218• 219 .

Yemada et al have reviewed the developments in-- the stereochemistry of

Schiff base metal 220complexes Metal complexes with unusual stereo-

chemistry and coordination number can be synthesized by choosing the

Schiff base and carefully controlling the experimental conditions221-224.

Schiff base complexes of uranyl ion have received much more

attention than those of the other oxocations225 • 226. A perusal through

the literature reveals that considerable interest has been paid to the

solution study of uranyl . 227-231 Schiff base complexes . In fact, quite

a large number of Schiff base complexes of uo�+ ion have been investi­

gated, those derived from salicylaldehyde and various amines being the

most thoroughly probed. Inner complexes of UO�+ ion with azomethine

derivatives such as 2-hydroxy-1-naph thal-4-iodoanilate, 4-methylsalicylal-

4-iodoanila te and 2-( 6:.bromo-z'.-hydroxy)-1-naphthalaminopyridinate having

tetragonal bi pyramidal, pentagonal bi pyramidal and hexagonal bi pyramidal232 structures have been reported . Solid uranyl chelates of Schiff bases

formed from aromatic .Q_-hydroxyaldehydes and carbazole amine have been233 isolated and reported . Cattalini et al have synthesized uranyl

complexes with dianions of salicylaldehyde Schiff bases in three different

ways and discussed the mechanism of uranyl ion catalysis of condensation

21

234 between aldehyde and amine . The reactions between terdentate Schiff

bases HsalenNRR' (derived from salicylaldehyde and N-substituted ethylene-

d. d235 diamine) and various uranyl salts have been stu 1e X-ray structural

analysis of uo2

csalenN(CH3)2

)2

shows a pentagonal bipyramidal environment

for the central uranium atom236 ' 237. Complexes of UO� + ion such as

uo2

(salophen)EtoH (where H2

salophen = N,N'-Q-phenylenebis(salicylaldimine)

and uo2

( salen) MeOH, (where H2

salen = N, N'-ethylene bis ( salicylaldimine)

have been prepared and the bonding of the quadridentate Schiff bases

in the complexes has been elucidated by X-ray studies238,239.

Uranyl complexes of some f3 -ketoximes and salicylaldimines have

been prepared, and their stability constants have been determined by

H t·t . t 240 p 1 rime ry El-Samahy et al have isolated uranyl complexes with

bi and tetrafunctional Schiff bases such as 1,2-(XC6

H4CHi:N)C6

H4 (where241 X = a-OH, .2-Me

2N, .2-0H or .2-N0

2) .

A series of new uranyl complexes with a di basic terdentate ligand

derived by the condensation of anthranilic acid and salicylaldehyde have 47 been reported . Uranyl complexes of arylideneanthranilic acid have

been isolated and characterized242. Salicylideneanthranilic acid is dibasic

terdentate whereas the other azomethines are monobasic bidentate. Saha

al have carried out studies on coordination compounds of uranyl ion with

N-(salicylidene)anthranilic acid243.

El-Haty et al have prepared and characterized uranyl complexes

of Schiff bases derived from salicylaldehyde and .2_-aminosalicylic acid,

22

phenylhydrazine, .2_-bromoaniline, _2-phenylenediamine and m-anisidine244 .

Stabilities of these complexes decrease with increasing basicity of the

azomethine group present in the Schiff bases. Uranyl ion forms 1: 2

adducts with Schiff bases obtained by condensing chloroanilines and

toluidines with salicylaldehyde245 The bonding with the metal in these

complexes takes place through the hydroxyl oxygen and imine nitrogen

of the ligand and the complexes have a coordination number of 8 with

a hexagonal bi pyramidal geometry.

2+ Synthesis and properties of a polymeric chelate of uo2

ion with

the Schiff base derived from 4, 4 ' -( 4, 4 ' -biphenylenebisazo )disalicylaldehyde

and aniline have been reported and this polychelate has a six coordinated 246 structure . El-Haty et al have prepared uranyl complexes of Schiff

bases derived from salicylaldehyde and certain amines containing one or

more heteroni trogen atoms24 7. These ligands are coordinated to the metal

ion through the azomethine nitrogen and the phenolic oxygen. Tezcan has

reported uranyl complexes of the mono and dianionic Schiff bases derived

from salicylaldehyde and various 2-hydroxyamines248 Prabhu et al have

reported eight coordinated orange red microcrystalline uranyl complexes

with Schiff bases derived from salicylaldehyde and substituted anilines249.

Saha et al have isolated and characterized uranyl complexes of N-(salicyli-. 250 251 dene )-L-valrne ' . The 1:1 Schiff base (L) prepared from 2,6-

diaminopyridine and salicylaldehyde has given uo2

L ( N03

)2

with uranyl

nitrate252. The ligand is terdentate coordinating through the azomethine

and amino nitrogen atoms and the phenolic oxygen atom.

Syamal

23

et al have reported uranyl complexes of Schiff bases

derived from ' 48substituted salicylaldehydes and 3-aminothiopheno�

Salicylidene-2-aminothiazole complexes of uranyl nitrate and uranyl acetate 253 also have been reported . Uranyl complexes of Schiff bases derived

from 2-amino-5-phenyl-1,3,4-thiadiazole and salicylaldehyde and

£-hydroxybenzaldehyde have been investigated by conductometric,

spectrophotometric and microanalytical methods254 .

Muvaffak et al have synthesized and characterized uranyl acetate

complexes with formazyl and azomethine series255 Monomeric and

polymeric Schiff bases derived from salicylaldehyde and 2, 5-dihydroxy-

terephthalaldehyde with some diamines, form complexes with uranyl ion

and the electrical conductance of these Schiff bases and their complexes

have been studied256 . N-acetylacetone-f3-alanine and N-acetylacetone-

anthranilic acid have formed 1: 1 complexes with uo�+ ion257 The

synthesis and characterization of the complex obtained by the reaction

of diethylenetriamine and 2, 6-diformyl-4-chlorophenol in presence of uranyl

ion have been reported 258 Uranyl complexes of �-( 2-pyrrolylmethylene­

amino) benzoic acid and 3-( 2-pyrrolylmethyleneamino)propionic acid have

been isolated and characterized259.

Schiff bases derived from dihydroxybenzaldehydes and diamines

react with uranyl ion to give stable complexes2 60. Uranyl complexes

of N-[1-( 2, 5-dihydroxyphenyl)ethylidene) ]anilines have been prepared

and screened for their fungicidal activity against two species of fungi261 .

Coordination compounds of uranyl acetate, uranyl chloride and uranyl

24

nitrate with 4-amino-3-aryl-5-cyano/carbethoxy-2-imino-4-thiazolines have

h . d262 been synthesized and c aracterize . The coordination sites of these

ligands are imino and amino nitrogen atoms. Bi and multinuclear uranyl

complexes of the tetraketones such as Q-H3cc6H4N(C(O)CH2

C(O)CH3)2 and263 1,1'-(2' ,6 '-pyridyl)bis-1,3-butanedione have been reported Uranyl

complex of 2, 5-pyrrolediylbis ( N-Q-hydroxyphenylaldimine) has been isolated

d h . d264 an c aracter1ze . Mononuclear and binuclear uranyl complexes have

been prepared using Schiff bases derived from Q-acetoacetylphenol,

2-acetyl-1, 8-dihydroxy-3, 6-dimethylnaphthalene, diacetylacetone and

benzoylacetylacetone and polyamines265. Potentiometric, magnetic,

conductance and spectral studies of solid complexes of uranyl ion with

N-Q-hy droxyacetop henonBc>imine-o-am inop henol have been conductect266.

Diagnostic features for the linkage isomerism of uranyl complexes of the

dioxine Schiff bases have been examined 267,

Schiff bases derived from 2, 6-diformyl-4-chlorophenol and

pol ya mines having two dissimilar coordination . sites can act as 268-271compartmental ligands forming mono and binuclear uranyl complexes

Khuhawar et al have reported uranyl complexes of tetradentate Schiff

bases derived from S-diketones and meso and dl -stilbenediamines272.

Hydrazone Schiff base complexes of uranyl ion are also known.

Uranyl complexes with salicylicarylidenehydrazides as ligands, have qeen

reported 273. Spectrophotometric and conductometric studies show that

1: 1 and 1: 2 ( metal : ligand) complexes have been formed with salicylic

salicylidenehydrazide and salicylic vanillinhydrazide. 2-Aceto-1-nap hthol-

25

2+ salicylhydrazone complexes of uo

2 1on with the metal to ligand ratios

2: 1, 1: 1 and 1: 2 have been prepared and their structural studies have

been done274

' 275. Dutta et al have isolated and characterized uranyl

complexes of salicylaldehyde aroyl/heteroaroylhydrazides276

. Isonicotina-

midosalicylaldimine (HL) complexes of uranyl ion having the composition

(where X = or have been prepared and

h t . d277

c arac erize . Syamal et al have synthesized and characterized uranyl

complexes of terdentate dibasic ONO donor Schiff bases derived from

.2-benzothiazole-carbohydrazide with salicylaldehyde and 2-hydroxy-1-

278 naphthaldehyde Uranyl complexes of salicylaldehyde-4-methoxybenzoyl-

hydrazone and diacetylbis( 4-methoxybenzoylhydrazone) have been isolated

and characterized by NMR studies279

.

Temerk et al

vanillidenebenzoic acid

have prepared

h d 'ct 280

y raz1 e

and studied uranyl complexes of

Uranyl complexes of a potential

ONNO tetradentate donor, butane-2, 3-dione-2-aminobenzoylhydrazone ( H2

L)

have been prepared and characterized 281

. At pH 6. 5-7 the ligand reacts

in the keto form to get [U02ITT

2UX

2J (where X = Cl, Br, N0

3, NCS, c104

At higher pH, [U02

L(H2

0)] is obtained in which the ligand

is in the enol form. Polymeric uranyl complexes with acyldihydrazones

have been preparect282. The ligands are coordinated in the enol form.

Quinquedentate chelating ligand 2, 6-diacetylpyridinebis ( 2 ' -pyridylhydrazone)

283 (H

2L) interacts with uo

2(N0

3)

2 to give [uo

2(H

2L)(N0

3)

2[uo

2(N0

3)

4J

Uranyl complexes With 2-benzoylpyridinebenzoylhydrazone and 2-benzoyl-

284 pyridinesalicylylhydrazone have also been prepared These two ligands

are monobasic terdentate NNO donors. Pentagonal bipyramidal complex

26

o f uranyl ion with 2 . , 6-diacetylpyridinebis ( 5!...chloro-2!..pyridylhydrazone)

285 has been reported . Singh et al

thiophene-2-aldehydethiosemicarbazone

have reported uranyl complexes of

286 (HL) with the composition uo2

L2

.

Chelation of the ligand to metal. is through -azomethine N and thiol S atoms.

Acetylacetonebis( 4!.phenyl thiosemicarbazone) complex of uranyl ion has been

synthesized and characterized, the ligand being a neutral dibasic

d ·ct t t SNNS donor287. qua ri en a e

of the macrocyclic ligand,

Yadev et al have reported a uranyl complex

2,6-diacetylpyridinebis(thiosemicarbazone) 288 •

Macrocyclic ligands derived by condensing benzil or diacetyl with diamine,

carboxyhydrazide and thiocarboxyhydrazide form stable solid uranyl

289 complexes Reddy et al have isolated and characterized a new uranyl

complex of 2-pyridinecarboxaldehydethiosemicarbazone290

Scope of the present investigation

The present investigation purports to synthesize and characterize

some uranyl complexes of certain polydentate Schiff base ligands. The

uranium salt employed exclusively for the present investigation is uranyl

nitrate hexahydrate. A total of 50 new complexes of uranyl nitrate with

some Schiff bases have been prepared and characterized on the basis

of their elemental analysis, molecular weight determination, electrical

conductance and magnetic susceptibility measurements, electronic and

infrared spectral studies. For convenience, the work presented in the

thesis is divided into seven chapters as detailed below.

27

Chapter I (this chapter) presents a brief introduction to the

chemistry of the actinides with special reference to that of uranium.

It also presents a brief survey of the coordination chemistry of uranyl

ion and the scope of the present investigation.

Chapter II describes the experimental details including a brief

description of the various physical methods and purities of the reagents

used for the present investigation. The methods of preparation of the

ligands and their structures are also given in this chapter.

Chapter III deals with the preparation and physicochemical studies

of uranyl nitrate complexes of some Schiff bases derived from 4-amino­

antipyrine and certain carbonyl compounds such as benzaldehyde, 2-nitro­

benzaldehyde, 3-nitrobenzaldehyde, 4-methylbenzaldehyde, 4-N, N-dimethyl­

aminobenzaldehyde, 2-hydroxybenzaldehyde, 2-hydroxy-1-naphthaldehyde,

acetylacetone, benzoylacetone and 4-benzoyl-3-methyl-1-phenylpyrazol-5-one.

Chapter IV describes the preparation and structure elucidation

of uranyl nitrate complexes of some heterocyclic Schiff bases derived

from furfural and 2-acetofuran and certain amino compounds such as

isonicotinylhydrazine, benzoylhydrazine, salicylylhydrazine, anthranilic

acid and 4-aminoantipyrine.

Chapter V is devoted to

the complexes of uranyl nitrate

4-pyridine carboxaldehydes and

the synthesis and characterization of

with some Schiff bases of 2, 3 and

certain amino compounds such as

isonicotinylhydrazine, benzoylhydrazine, salicylylhydrazine and 4-amino­

anti p yrine.

28

Chapter VI presents the preparation and structural studies of

uranyl nitrate complexes of some Schiff bases derived by condensing

vanillin and veratraldehyde with certain amino compounds such as

benzoylhydrazine, salicylylhydrazine, anthranilic acid, 2-am inop henol

and 4-aminoantipyrine.

Chapter VII deals with the preparation and characterization of

uranyl nitrate complexes of some Schiff bases derived from 2-hydroxy-1-

naphthaldehyde and certain amino compounds such as isonicotinylhydrazine,

benzoylhydrazine, salicylylhydrazine,

2-aminobenzyl alcohol, 2-aminop henol,

and 3-aminopyridine.

5-aminouracil,

3-aminop henol,

anthranilic acid,

2-aminopyridine