introduction and scope of the present...
TRANSCRIPT
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