Studies on some thorium(IV) complexes with high coordination numbers derived from semicarbazones of 4-aminoantipyrine

Article abstract of DOI:10.1081/SIM-200026274

The interaction of thorium(IV) salts with 4[N-(benzylidene)amino]antipyrine semicarbazone (BAAPS), 4[N-(4′-methoxybenzylidene)amino] antipyrine semicarbazone (MBAAPS), 4[N-(4′-dimethoxyaminobenzylidene)amino]antipyrine semicarbazone (DABAAPS), 4[N-(2′-nitrobenzylidene)amino]antipyrine semicarbazone (2′-NO₂BAAPS), and 4[N-(3′- nitrobenzylidene)amino]antipyrine semicarbazone (3′-NO₂BAAPS) in non-aqueous solvents resulted in the formation of [ThL₂X ₄] (X = Cl, Br, or NCS), [ThL₂I₂]I₂, [ThL₂](ClO₄)₂ or [ThL(NO₃) ₄] (L = BAAPS, MBAAPS, DABAAPS, 2-NO₂BAAPS, or 3-NO ₂BAAPS). All of these compounds were characterized by elemental analyses, electrical conductivity, IR, and thermal methods. X-ray powder diffraction studies of a representative complex were also undertaken. Th(IV) displays the coordination numbers 6, 8, 10, and 11 in these compounds depending on the nature of the coordinated anion and the stoichiometry.

Full text of DOI:10.1081/SIM-200026274

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Studies on Some
Thorium(IV) Complexes
with High Coordination
Numbers Derived from
Semicarbazones of
4‐Aminoantipyrine
Ram K. Agarwal a , Indranil Chakraborti b &
Himanshu Agarwal b
a Department of Chemistry, School of Pure and
Applied Sciences , The University of the South
Pacific , P.O. Box 1168, Suva, Fiji Islands
b Department of Chemistry , Lajpat Rai
Postgraduate College , Sahibabad, Ghaziabad,
India
Published online: 16 Nov 2010.
To cite this article: Ram K. Agarwal , Indranil Chakraborti & Himanshu Agarwal
(2004) Studies on Some Thorium(IV) Complexes with High Coordination Numbers
Derived from Semicarbazones of 4‐Aminoantipyrine, Synthesis and Reactivity
in Inorganic and Metal-Organic Chemistry, 34:8, 1431-1452, DOI: 10.1081/
SIM-200026274
To link to this article: http://dx.doi.org/10.1081/SIM-200026274
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 8, pp. 1431–1452, 2004
Studies on Some Thorium(IV) Complexes
with High Coordination Numbers Derived
from Semicarbazones of 4-Aminoantipyrine
2
Ram K. Agarwal,1, Indranil Chakraborti,
*
and Himanshu Agarwal2
1Department of Chemistry, School of Pure and Applied Sciences,
The University of the South Pacific, Suva, Fiji Islands
2Department of Chemistry, Lajpat Rai Postgraduate College, Sahibabad,
Ghaziabad, India
ABSTRACT
The interaction of thorium(IV) salts with 4[N-(benzylidene)amino]anti-
pyrine semicarbazone (BAAPS), 4[N-(40-methoxybenzylidene)amino]
antipyrine semicarbazone (MBAAPS), 4[N-(40-dimethoxyaminobenzyl-
idene)amino]antipyrine semicarbazone (DABAAPS), 4[N-(20-nitrobenzyl-
idene)amino]antipyrine semicarbazone (20-NO2BAAPS), and 4[N-(30-
nitrobenzylidene)amino]antipyrine semicarbazone (30-NO2BAAPS) in
non-aqueous solvents resulted in the formation of [ThL2X4] (X ¼ Cl,
Br, or NCS), [ThL2I2]I2, [ThL2](ClO4)2 or [ThL(NO3)4] (L ¼ BAAPS,
*
Correspondence: Ram K. Agarwal, Department of Chemistry, School of Pure and
Applied Sciences, The University of the South Pacific, P.O. Box 1168, Suva, Fiji
Islands; E-mail: agarwal_r@usp.ac.fj.
1431
DOI: 10.1081/SIM-200026274
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

1432
Agarwal, Chakraborti, and Agarwal
MBAAPS, DABAAPS, 2-NO2BAAPS, or 3-NO2BAAPS). All of these
compounds were characterized by elemental analyses, electrical conduc-
tivity, IR, and thermal methods. X-ray powder diffraction studies of a
representative complex were also undertaken. Th(IV) displays the
coordination numbers 6, 8, 10, and 11 in these compounds depending
on the nature of the coordinated anion and the stoichiometry.
Key Words: Thorium(IV); Semicarbazones; Complexes; Coordination
number.
INTRODUCTION
The coordination polyhedra of actinide ions have been extensively inves-
tigated and sufficiently well characterized in the solid state especially by x-ray
investigations. The contraction of the ionic radius with increasing atomic
number is related to the maximum obtainable coordination number with tro-
polonato and 8-hydroxyquinolinato ligands. It is possible to prepare Th(IV)
and U(IV) 10-coordinated complexes and only eight coordinated complexes
of Np(IV) and Pu(IV) with these ligands. Thorium(IV) with an atomic
˚
radius of 1.65 A and a high charge fulfills the optimum conditions for high
coordination.[1] Thorium(IV) is an example of a typical hard Lewis acid, as
compared to the tendency to coordination of oxygen and sulfur donors and
also of nitrogen and phosphorus donors.[2,3] Both oxygen and nitrogen have
an appreciable tendency to coordinate to thorium(IV) although complexes
containing O-donors are more common than those containing N-donors. In
thorium(IV) complexes, the coordination number of thorium(IV) varies from
6 to 12. The coordination numbers 6, 8, 10, 11, and 12 are usually found in
thorium(IV) complexes, while the coordination numbers 7 and 9 are rather
uncommon for thorium(IV) complexes.[4,5] In the literature a good number
of thorium(IV) complexes of Schiff bases are reported,[6,7] but comparatively
less is known about thorium(IV) complexes of semicarbazones. In view of
this, the present studies are devoted to the preparation and characterization
of 30 coordination compounds of thorium(IV) with 4[4-(benzylidene)amino]
antipyrine semicarbazone (BAAPS), 4[N-(40-methoxybenzylidene)amino]
antipyrine semicarbazone (MBAAPS), 4[N-(40-dimethoxyaminobenzylidene)
amino]antipyrine semicarbazone (DABAAPS), 4[N-(20-nitrobenzylidene)
amino]antipyrine semicarbazone (20-NO2BAAPS), and 4[N-(30-nitrobenzyl-
idene)amino]antipyrine semicarbazone (30-NO2BAAPS) (Fig. 1). In these
compounds thorium(IV) displays the coordination numbers 6, 8, 10, or 11
depending on the nature of the coordination anion and the stoichiometry.

Thorium(IV) Complexes
1433
Figure 1. Structure of ligands.
EXPERIMENTAL
Materials
Thorium(IV) nitrate was obtained from BDH. Thorium(IV) perchlorate
was prepared as reported.[8] Crystals of ThX4 (X ¼ Cl, Br, I, or NCS) were
prepared by known methods.[9] All the thorium(IV) salts are hygroscopic
and were stored in a desiccator over concentrated sulfuric acid. 4-Aminoanti-
pyrine (Koch & Light), benzaldehyde, 4-methoxybenzaldehyde, 4-dimethyl-
aminobenzaldehyde,
2/3-nitrobenzaldehyde,
and
semicarbazide
hydrochloride (CDH) were obtained commercially and used as received.
The following semicarbazones (Fig. 1) were prepared in the laboratory.
1. 4[4-(benzylidene)amino]antipyrine
(C19H20N6O).
semicarbazone
(BAAPS),
2. 4[N-(40-methoxybenzylidene)amino]antipyrine
(MBAAPS), (C19H22N6O2).
semicarbazone
3. 4[N-(40-dimethoxyaminobenzylidene)amino]antipyrine semicarba-
zone (DABAAPS), (C21H25N7O).

1434
Agarwal, Chakraborti, and Agarwal
4. 4[N-(20-nitrobenzylidene)amino]antipyrine
NO2BAAPS) (C19H19N7O3).
5. 4[N-(30-nitrobenzylidene)amino]antipyrine
NO2BAAPS) (C19H19N7O3).
semicarbazone
semicarbazone
(20-
(30-
Synthesis of Semicarbazones
All five derivatives were synthesized in two steps.[10]
1. A solution of an aromatic aldehyde (1 mmol) in absolute ethanol
(20 mL) was mixed with 4-aminoantipyrine (1.1 mmol, 0.2234 g) in
the same solvent (20 mL) and the reaction mixture was refluxed for
2–3 hr. On cooling, a yellow crystalline product separated, which
was filtered and recrystallized in the same solvent.
2. Semicarbazones were prepared by the following method. Semicarba-
.
zide hydrochloride (H2NNHCONH2 HCl) (15 g, 0.134 mol) and
sodium acetate (CH3COONa) (13 g, 0.15 mol) were dissolved in
60 mL distilled water and mixed with the corresponding Schiff
base (0.1 mol) [prepared in (1)] in ethanol (25 mL). The mixture
was refluxed on a water bath for 1 hr. On cooling the contents, the
semicarbazones crystallized out. They were filtered, washed with
50% ethanol, and recrystallized from ethanol. The obtained light
yellow crystals were filtered and dried at ꢀ60 8C in an electric oven.
Synthesis of the Complexes
[ThL2X4] (X ¼ Cl, Br, or NCS) (L ¼ BAAPS, MBAAPS, DABAAPS,
20-NO2BAAPS, or 30-NO2BAAPS)
A methanolic solution (10 mL) of ThX4 (X ¼ Cl, Br, and NCS) (1 mmol)
was added to the respective ligand solution (2.1 mmol, 20 mL of methanol)
dropwise. The reaction mixture was refluxed for 2 hr on a water bath. Solid
compounds were obtained after reducing the volume of the reaction mixture
to 1/2 under a fan. The precipitate was filtered by suction, washed with
methanol, and dried under vacuo over P4O10.
[ThL2I2]I2 (L ¼ BAAPS, MBAAPS, DABAAPS, 20-NO2BAAPS, or
30-NO2BAAPS)
A methanolic solution (10 mL) of ThI4 (1 mmol, 0.74 g) was added to
the respective ligand solution (2.1 mmol, 20 mL of methanol) dropwise.

Thorium(IV) Complexes
1435
The reaction mixture was refluxed for 2 hr on a water bath. The reaction
mixture was left overnight for complete precipitation. The precipitate was fil-
tered by suction, washed with methanol, and dried under vacuo over P4O10.
[ThL2](ClO4)4 (L ¼ BAAPS, MBAAPS, DABAAPS, 20-NO2BAAPS,
or 30-NO2BAAPS)
To a solution of Th(ClO4)4 (1 mmol, 0.63 g) in isopropyl alcohol (10 mL)
was added a hot solution of the respective ligand (2 mmol) in the same solvent
(10 mL). In case of BAAPS, MBAAPS, and DABAAPS, the desired complex
was obtained immediately. But in case of 20-NO2BAAPS and 30-NO2BAAPS
the reaction mixture was refluxed for 1–2 hr. On cooling to room temperature
the desired complexes were obtained. The solid products were filtered, washed
with isopropyl alcohol, and dried in vacuo over P4O10.
[ThL(NO3)4] (L ¼ BAAPS, MBAAPS, DABAAPS, 20-NO2BAAPS,
or 30-NO2BAAPS)
To a solution of Th(NO3)4 (1 mmol, 0.56 g) in ethyl acetate (15 mL) was
added the respective ligand (1.1 mmol) in the same solvent (10 mL) and the
reaction mixture was refluxed for about 1 hr and then left for overnight at
room temperature. Fine crystalline products were obtained which were
filtered by suction, washed with ethyl acetate, and finally dried in vacuo
over P4O10.
All of the physico-chemical measurements and analyses were performed
as reported previously.[4,5] Infrared spectra in the range of 4000–200 cm21
were measured on a Perkin–Elmer Infracord Spectrophotometer model 521
in Nujol mulls at the Department of Chemistry, University of Delhi. We
have not tried NMR studies of present studies. Thermogravimetric analyses
were carried with a Santon Redcraft Thermobalance Model TG-750 thermo-
balance in open air. We did not succeed in obtaining single crystals.
RESULTS AND DISCUSSION
The physical characteristics and chemical analysis of all of the five semi-
carbazones are summarized in Table 1. The interaction of thorium(IV) salts
with BAAPS, MBAAPS, DABAAPS, 20-NO2BAAPS, or 30-NO2BAAPS
results in the formation of ThL2X4 (X ¼ Cl, Br, or NCS] (L ¼ BAAPS,
MBAAPS, DABAAPS, 20-NO2BAAPS, or 30-NO2BAAPS); [ThL2I2]I2,

1436
Agarwal, Chakraborti, and Agarwal

Thorium(IV) Complexes
1437
[ThL2](ClO4)4 and [ThL(NO3)4] according to the following general
equations.
Methanol
þ2L ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ! ½ThL2X4ꢁ
ThX4
ðX ¼ Cl; Br or NCSÞ
ð1Þ
Reflux for 2 hr and cool
Methanol
ThI4 þ 2L ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ! ½ThL2I2ꢁI2
Isopropyl alcohol
ThðClO4Þ4 þ 2L ꢀꢀꢀꢀꢀꢀꢀꢀꢀ! ½ThL2ꢁðClO4Þ4
Reflux for 1–2 hr
ð2Þ
ð3Þ
ð4Þ
Reflux for 2 hr and cool
Ethyl acetate
ThðNO3Þ4 þ L ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ! ½ThLðNO3Þ4ꢁ
Reflux for 1 hr and left
stand overnight
The analytical data of these complexes are given in Table 2. The complexes
are anhydrous, which is evident from the analytical, infrared, and thermal
studies. All of the complexes are quite stable and can be stored for long
periods except the thorium(IV) iodide complexes, which decompose
slowly at room temperature with the evolution of iodine vapours. All of
the complexes are generally soluble in common organic solvents. Among
the thorium(IV) complexes, the chloro, bromo, nitrato, and thiocyanato
complexes are non-electrolytes (Table 2) in PhNO2, whereas the iodo and
perchlorato complexes dissociate in this solvent. The iodo complexes
appear to be a 1 : 2, while the perchlorato complexes are 1 : 4 electrolytes.
Data on the molecular weight of the complexes in freezing PhNO2 are con-
tained in Table 2, along with values calculated on the basis of the estab-
lished formula of the complexes. The ratio of molecular weight observed
for [ThL2X4] (X ¼ Cl, Br, or NCS; L ¼ BAAPS, MBAAPS, DABAAPS,
20-NO2BAAPS, or 30-NO2BAAPS) and [ThL(NO3)4] to that calculated is
ꢀ0.98 which shows that the complexes are monomeric in solution. In the
cases of [ThL2I2]I2 and [ThL2](ClO4)4, the ratios are ꢀ0.33 and ꢀ0.20,
respectively. These data further support that three species are formed in
the former complexes and five species are formed in the latter set of
complexes.
Infrared Spectra
The infrared spectra of all of the five semicarbazones derived from
4-aminoantipyrine are too complex to make definite band assignments.
Empirical assignments by referring to the group frequencies may not be effec-
tive since coupling between various modes of vibration are expected as a
result of resonance in the pyrazolone ring. Infrared absorption of the five semi-
carbazones of 4-aminoantipyrine have been assigned by a comparison of their

1438
Agarwal, Chakraborti, and Agarwal

Thorium(IV) Complexes
1439

1440
Agarwal, Chakraborti, and Agarwal

Thorium(IV) Complexes
1441
spectra with those of antipyrine, 4-aminoantipyrine[11–13] and some previous
works on semicarbazones.[10,14,15]
In these complexes, as expected, n(NH2) of the hydrazinic nitrogen of
semicarbazide (ꢀ1622 cm21) is absent in the infrared spectra of BAAPS,
MBAAPS, DABAAPS, 20-NO2BAAPS, and 30-NO2BAAPS.[16] It has also
been observed that the amide-II band in the complexes is shifted towards
the lower energy side compared to that of the semicarbazone. The effect is
due to the electron density drift from the hydrazinic nitrogen to metal
ion.[17] The characteristic absorption of the carbonyl group in BAAPS,
MBAAPS, DABAAPS, 20-NO2BAAPS, or 30-NO2BAAPS is observed in
the 1700–1680 cm21 region.[18]. In the complexes, these bands are shifted
toward lower energy in the 1650–1640 cm21 region (Table 3). The amide-
II band in the free ligands has been observed at ꢀ1565 cm21. In all the
present complexes, this band is also shifted towards lower wave numbers
by ꢀ30 cm21. This observation suggests coordination through the carbonyl
oxygen atom. The strong bands at ꢀ1600 cm21 in these semicarbazones
apparently have a large contribution from the n(C55N) mode of the semicar-
bazone moiety.[19] This has been observed as a blue-shift in the position of the
C55N band in all complexes as compared to the free ligands. Another strong
band was observed at ꢀ1610 cm21 due to azomethine C55N absorption. On
complexation this band is shifted towards the lower frequency region,
clearly indicating the coordination through the azomethine N atom.[20–22] In
the far-infrared region the bands due to n(Th–N)/n(Th–O) are also
observed[23,24] (Table 3). From these facts, it is clearly indicated that these
ligands serve as tridentate ligands, coordinating through the carbonyl O;
hydrazone N and azomethine N atoms.
The occurrence of two strong bands at ꢀ1070 and 620 cm21 in the spectra
of the [ThL2](ClO4)4 complexes attributed to n3 and n4 vibrations of ionic per-
chlorate suggests[25–27] the presence of a perchlorate group outside the coordi-
nation sphere in the complex[4,26] (Table 4).
For thorium(IV) nitrate complexes, the occurrence of two strong absorp-
tions in the 1540–1514 and 1295–1270 cm21 regions is attributed to n4 and n1
modes of vibration of the covalently bonded nitrate group, respectively,
suggesting that the nitrate groups are inside the coordination sphere.[28,29]
Other absorption bands associated with the covalent nitrate groups are also
observed in the spectra of the complexes. The spectral bands of
[ThL(NO3)4] (L ¼ semicarbazones) were compared with the known bands
[30]
.
of Th(NO3)4 5H2O
i.e. 150 (n4), 1290 (n1), 1030 (n2), 808(n6), 745 (n3)
and 715 cm21(n5), in which the bidentate character of the nitrato groups
has been established by x-ray[31] and neutron diffraction studies.[32,33] It is
inferred that the nitrate groups in these complexes also behave as bidentate
ligands[33–35] (Table 5).

1442
Agarwal, Chakraborti, and Agarwal

Thorium(IV) Complexes
1443

1444
Agarwal, Chakraborti, and Agarwal

Thorium(IV) Complexes
1445
Table 4. Infrared absorption frequencies (cm21) of the perchlorato
group in thorium(IV) perchlorato complexes of semicarbazones.
Complexes
n3
n4
[Th(BAAPS)2](ClO4)4
1080 vs
1085 s
1100 s
620 s
622 s
625 s
620 s
622 vs
[Th(MBAAPS)2](ClO4)4
[Th(DABAAPS)2](ClO4)4
[Th(20-NO2BAAPS)2](ClO4)4
[Th(30-NO2BAAPS)2](ClO4)4
1080 s, br
1096 vs, br
The C–N stretching frequency in the thiocyanato complexes of thorium
appears in the 2070–2040 cm21 region, which lies on the borderline for dis-
tinguishing,[36–38] although the high relative intensity of the band in these
cases suggests that the thiocyanate groups are N-bonded.[37,38] The frequency
of the C–S stretching vibration has also been used to diagnose the bonding
mode in thiocyanates.[37,38] The C–S band identified in the 840–780 cm21
region, further confirms that the thiocyanate group is almost certainly
N-bonded,[39] the N–C–S bending (n2) is also identified in these complexes
(Table 6).
In the halide complexes the n(Th–Cl) vibration has been assigned at the
290–250 cm21 region[40] while the n(Th–Br) and n(Th–I) frequencies could
not be assigned because they are out of the region studied here.
X-Ray Powder Diffraction Studies
X-ray powder diffraction studies of [Th(BAAPS)(NO3)4] have been done
˚
on a model PW 1140 Phillips x-ray diffractometer with CuKa ¼ 1.54178 A. It
was found that this complex belongs to the monoclinic crystal system with
˚
o
˚
˚
a ¼ 8.910(1) A, b ¼ 11.134(6) A; c ¼ 11.652(3) A, and b ¼ 84.766(7)
Thermal Studies
The thermal studies results of the Th(IV) complexes of BAAPS,
MBAAPS, DABAAPS, and 20-NO2BAAPS are presented in Table 7. The
TG curves of the Th(IV) complexes do not show the presence of water mol-
ecules, either in or out of the coordination sphere. The thermogravimetric
curves of the chloro, bromo, and thiocyanato complexes indicate that in
step 1 only one molecule of ligand molecule is lost, while at ꢀ430 8C, the
remaining ligand molecule has also been lost. Finally, at ꢀ605 + 5 8C,

1446
Agarwal, Chakraborti, and Agarwal

Thorium(IV) Complexes
1447
Table 6. Infrared absorption frequencies (cm21) of the isothiocyanato group in
thorium(IV) isothiocyanato complexes of semicarbazones.
Complexes
n1
n3
n2
[Th(BAAPS)2(NCS)4]
2051 vs
2050 vs
2055 vs
2045 vs
2065 vs
757 m
760 m
755 m
820 m
832 m
480 m
475 m
482 m
475 m
480 w
[Th(MBAAPS)2(NCS)4]
[Th(DABAAPS)2(NCS)4]
[Th(20-NO2BAAPS)2(NCS)4]
[Th(30-NO2BAAPS)2(NCS)4]
oxohalide and oxothiocyanato formation takes place. The thorium(IV) nitrate
complexes decompose in the 280–425 8C temperature region, losing the
ligand molecule. Finally, ThO2 is obtained as residual mass at ꢀ610 8C.
The thermogravimetric curve of [Th(DABAAPS)2](ClO4)4 shows that the
complex starts to decompose at 215 8C and decomposition continues up to
605 8C, after which ThO2 remains as residue (Table 7). From the pyrolysis
curve, it is clear that no stable intermediate perchlorate complex has been
formed in this species. For the iodo complexes, which form a sticky mass,
we have not studied the thermal analyses. The analyses of the thermograms
indicate the following decomposition schemes:
½ThL2X4ꢁ ꢀ! ½ThLX4ꢁ ꢀ! ThX4 ꢀ! ThOX2
ðX ¼ Cl; Br, or NCSÞðL ¼ BAAPS; MBAAPS; DABAAPS;
or 20-NO2BAAPSÞ
½ThLðNO3Þ4ꢁ ꢀ! ThðNO3Þ4 ꢀ! ThO2
ðL ¼ BAAPS; MBAAPS ; DABAAPS; or 20-NO2BAAPSÞ
½ThðDABAAPSÞ2ꢁðClO4Þ4 ꢀ! ThO2
In general, if the minimum TG decomposition temperature is taken as a rough
criterion of thermal stability then the order of stability of the Th(IV) com-
plexes is: NO3 . Cl . Br . NCS . ClO4.
Stereochemistry
The preferred coordination number of Th(IV) is 6 or 8, but higher coordi-
nation numbers have also been observed.[41,42] In the chloro, bromo, and
thiocyanato complexes, conductance and molecular weight determinations
suggest that the complexes are non-ionic in nature and do not dissociate in
nitrobenzene solvent. Thus, in the case of the BAAPS, MBAAPS,

1448
Agarwal, Chakraborti, and Agarwal

Thorium(IV) Complexes
1449
Figure 2. Suggested structures of thorium(IV) complexes of semicarbazones.
DABAAPS, 20-NO2BAAPS, and 30-NO2BAAPS complexes of ThX4 (X ¼ Cl,
Br, or NCS) the coordination number of Th(IV) is found to be 10. In case of
iodo complexes the 1 : 2 electrolytic nature suggests that two iodine atoms
are present outside the coordination sphere and, hence, the coordination
number of Th(IV) in [Th(L2)I2]I2 [L ¼ BAAPS, MBAAPS, DABAAPS,
20-NO2BAAPS, or 30-NO2BAAPS] is found to be eight.
It has been found from a single crystal x-ray structure determination of
.
Th(NO3)4 5H2O that the nitrato groups are linked to thorium through two
oxygen atoms, each nitrato group thus functioning as a bidentate ligands. In
the [Th(L)(NO3)4] [L ¼ BAAPS, MBAAPS, DABAAPS, 20-NO2BAAPS, or
30-NO2BAAPS] complexes, the Th(IV) atom is surrounded by nine oxygens
(eight oxygens from four nitrato groups and one oxygen from the amide
group) and two nitrogen atoms of azomethine groups and thus the products
have a coordination number of 11 for the thorium atom. In [ThL2](ClO4)4
(L ¼ BAAPS, MBAAPS, DABAAPS, 20-NO2BAAPS, and 30-NO2BAAPS)
the conductance, molecular weight, and IR studies reveal that all four per-
chlorato groups are present outside the coordination sphere, hence suggesting
the presence of six-coordinated Th(IV) in these complexes. The proposed
structures of the present thorium(IV) complexes are given in Fig. 2.

1450
Agarwal, Chakraborti, and Agarwal
ACKNOWLEDGMENTS
One of the authors (R.K.A.) is thankful to the University Grants Commis-
sion, New Delhi, for financial assistance and Mr. Steven Sutcliffe, Chief Tech-
nician, Chemistry Department, The University of the South Pacific for his
assistance in finalizing the paper.
REFERENCES
1. Lippard, S.J. Eight coordination chemistry. Prog. Inorg. Chem. 1967, 8,
109.
2. Bagnall, K.W. The coordination chemistry of the actinide halides. Coord.
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Received April 30, 2001
Accepted April 6, 2004