Versatile chelating behavior of benzil bis(thiosemicarbazone) in zinc, cadmium, and nickel complexes

Article abstract of DOI:10.1021/ic035461a

Reactions of benzil bis(thiosemicarbazone), LH₆, with M(NO ₃)2·nH₂O (M = Zn, Cd, and Ni), in the presence of LiOH·H₂O, show the versatile behavior of this molecule. The structure of the ligand, with the thiosemicarbazone moieties on opposite sides of the carbon backbone, changes to form complexes by acting as a chelating molecule. Complexes of these metal ions with empirical formula [MLH₄] were obtained, although they show different molecular structures depending on their coordinating preferences. The zinc complex is the first example of a crystalline coordination polymer in which a bis(thiosemicarbazone) acts as bridging ligand, through a nitrogen atom, giving a 1D polymeric structure. The coordination sphere is formed by the imine nitrogen and sulfur atoms, and the remaining position, in a square-based pyramid, is occupied by an amine group of another ligand. The cadmium derivative shows the same geometry around the metal ion but consists of a dinuclear structure with sulfur atoms acting as a bridge between the metal ions. However, in the nickel complex LH₆ acts as a N₂S₂ ligand yielding a planar structure for the nickel atom. The ligand and its complexes have been characterized by X-ray crystallography, microanalysis, mass spectrometry, IR, ¹H, and ¹³C NMR spectroscopies and for the cadmium complex by ¹¹³Cd NMR in solution and in the solid state.

Full text of DOI:10.1021/ic035461a

Inorg. Chem. 2004, 43, 5222−5230
Versatile Chelating Behavior of Benzil Bis(thiosemicarbazone) in Zinc,
Cadmium, and Nickel Complexes
a
,†
Elena Lo´pez-Torres,† M Antonia Mendiola,* Ce´sar J. Pastor,‡ and Beatriz Souto Pe´rez‡
Departamento de Qu´ımica Inorga´nica, UniVersidad Auto´noma, Madrid-28049, Spain, and
SerVicio Interdepartamental de InVestigacio´n, UniVersidad Auto´noma, 28049-Madrid, Spain
Received December 19, 2003
Reactions of benzil bis(thiosemicarbazone), LH , with M(NO ) ‚nH O (M ) Zn, Cd, and Ni), in the presence of
6
3 2
2
LiOH‚H O, show the versatile behavior of this molecule. The structure of the ligand, with the thiosemicarbazone
2
moieties on opposite sides of the carbon backbone, changes to form complexes by acting as a chelating molecule.
Complexes of these metal ions with empirical formula [MLH ] were obtained, although they show different molecular
4
structures depending on their coordinating preferences. The zinc complex is the first example of a crystalline
coordination polymer in which a bis(thiosemicarbazone) acts as bridging ligand, through a nitrogen atom, giving a
1D polymeric structure. The coordination sphere is formed by the imine nitrogen and sulfur atoms, and the remaining
position, in a square-based pyramid, is occupied by an amine group of another ligand. The cadmium derivative
shows the same geometry around the metal ion but consists of a dinuclear structure with sulfur atoms acting as
a bridge between the metal ions. However, in the nickel complex LH acts as a N S ligand yielding a planar
6
2 2
structure for the nickel atom. The ligand and its complexes have been characterized by X-ray crystallography,
microanalysis, mass spectrometry, IR, 1H, and 13C NMR spectroscopies and for the cadmium complex by 113Cd
NMR in solution and in the solid state.
Introduction
metal-enzymes have stimulated the design of synthetic
polydentate ligands that mimic the coordination environment
of metal ions in proteins. Zn(II) usually favors tetrahedral
coordination; in this respect a recent review4 cited over 600
Zn(II) complexes which are predominantly tetrahedral.
Recently, a zinc coordination polymer with this geometry
around the metal ion has been described.5 Among the less
common five-coordinate complexes, trigonal bipyramidal
(tbp) geometry occurs more frequently than square-based
pyramidal (sbp). The latter case is usually sustained by a
basal plane of the donor atoms in a tetradentate macrocycle,
with the apical position occupied by a terminal ligand such
as pyridine or chloride.
Polynuclear complexes from thiosemicarbazones are not
very common; however, some derivatives of [1 + 1]
condensation products have been published. A bridging sulfur
atom is observed in the polymeric structures of copper and
lead complexes of 1-methylisatin 3-thiosemicarbazone and
2-acetylpyridine-4-N-methylthiosemicarbazone, respectively.6,7
The synthesis of coordination polymers is currently of
great interest as a method for the construction of new
supramolecular architectures, due to their properties such as
luminescence and conductivity and their applications in
catalysis.1 Factors influencing the formation of coordination
polymers are not well understood; for a simple bifunctional
ligand, the metal ratio is important in the construction of
novel architectures2 and various other factors such as the
nature of the metal ions and the counteranions may also
influence the formation of one structure over the other.
Moreover, experimental conditions can add complexity to
the problem and variation of these may lead to polymorph-
ism.3 The fascinating structural and catalytic properties of
* Author to whom correspondence should be addressed. E-mail:
antonia.mendiola@uam.es.
† Departamento de Qu´ımica Inorga´nica.
‡ Servicio Interdepartamental de Investigacio´n.
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5222 Inorganic Chemistry, Vol. 43, No. 17, 2004
10.1021/ic035461a CCC: $27.50 © 2004 American Chemical Society
Published on Web 07/27/2004

Zn, Cd, and Ni Benzil Bis(thiosemicarbazone)s
A polymeric structure of a zinc complex is formed by sulfur
and oxygen atoms from 2-acetylpyridine N-oxide 4-N-
methylthiosemicarbazone bridging between ZnI2 units giving
a tetrahedral coordination for the metal ion,8 and two bridging
oxygen atoms provided by the thiosemicarbazone and an
acetate group are observed in a polymeric zinc(II) complex,
in which the pentacoordinated geometry of the metal atom
is completed by the terminal amine nitrogen.9 This group,
besides the sulfur atom, is also involved in the coordination
in the salicylaldehyde thiosemicarbazonato heterooctametallic
complex containing a cyclic Ru4Ni4 core.10
Most of the cadmium(II) thiosemicarbazone complexes
studied by X-ray diffractometry are adducts of cadmium
dihalide; only a few of them contain thiosemicarbazonate
anions. The first complex with the last situation is that with
pyridinethiosemicarbazone in which the two N,N,S-coordi-
nate ligands give the metal ion a highly distorted octahedral
coordination polyhedron. A polynuclear complex [Cd3-
(HMeOSTSC)4](OAc)2‚0.5DMSO‚2H2O is characterized, in
which cadmium ions are bridged by the oxygen atoms of
the deprotonated phenolic hydroxy groups belonging to the
four TSC ligands. Each terminal Cd(II) is additionally
coordinated to N and S atoms of the two TSC ligands in a
Z-configuration giving a [CdN2O2S2] kernel with distorted
octahedral geometry, while the central metal ion attains a
coordination number of 8 through additional bonding to the
four methoxy group, giving a triangular dodecahedral
coordination geometry.15 Recently, the complex with pyra-
zineformamide N(4)-methylthiosemicarbazone has been re-
ported,27 where the cadmium ion is hexacoordinated by two
ligands acting as a tridentate through the imine and the
pyridine nitrogen atoms, as well as the thiolate sulfur.
Structural data for the [MN2S2] complex unit resulting
from the coordination of bis(thiosemicarbazones) with cop-
per(II) and nickel(II) are well-known. Both ions preferably
form mononuclear planar complexes.11-14 Since Zn(II) usu-
ally favors tetrahedral coordination, the question arises how
the conformation of these kind of ligands affects the structure
of the corresponding zinc complexes. Therefore, these
complexes should be stabilized either by additional coordina-
tion of monodentate Lewis bases giving a five-coordinated
zinc atom15-19 or through dimerization if a bidentate group
is present.20,21 An example of a bis(thiosemicarbazone) acting
as a bridge between two zinc atoms is the complex derived
from 1-phenylglyoxal bis(3-piperidylthiosemicarbazone), in
which the anionic thiosemicarbazone moieties lead to a
[ZnN3S2] unit for each atom in a binuclear compound.22
Polymeric compounds can be obtained if an additional Lewis
base acts as a bridge ligand.23-26
1
113Cd has a spin of /2 (thus, no quadrupolar contribution
to NMR relaxation which broadens signals) and an abun-
dance of 12.26% (compared to 1.11% for 13C). 113Cd has a
demonstrated chemical shift range of over 900 ppm, and the
value of the chemical shift has been shown to depend on
the nature, number, and geometric arrangement of the atoms
coordinated to cadmium. This enables one to apply 113Cd
NMR spectroscopy as a probe of the metal in binding sites
in biological systems and coordination compounds. When
cross-polarization magic angle spinning (CP MAS) 113Cd
NMR spectroscopy is combined with X-ray crystallography,
an excellent opportunity is provided to study and correlate
metal ion geometry with the chemical shifts. 113Cd NMR
signals in the solid state or in solution are able to describe
the ligand and its geometry about the cadmium atom.28-31
In a previous work32 we have established that benzil bis-
(thiosemicarbazone) (Chart 1), LH6, requires planar coordi-
nation for a cadmium derivative. This complex consists of
octahedral units, in which the equatorial positions are
occupied by the neutral ligand and the axial ones by
monodentate nitrate groups. This is the reason formation of
tetrahedral complexes should not occur, but it is easy to get
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Inorganic Chemistry, Vol. 43, No. 17, 2004 5223

Lo´pez-Torres et al.
Chart 1. Drawing of LH6
with methanol, and vacuum-dried (95%). (Anal. Found: C, 45.34;
H, 3.60; N, 19.88; S, 14.98. Calcd for ZnC16H14N6S2: C, 45.78;
H, 3.34; N, 20.03; S, 15.26.) MALDI-TOF+ (m/z): 419.1, [ZnLH4
1
+ 1]+. H NMR (DMSO-d6): δ 7.5-6.9, m. 13C NMR (DMSO-
d6): δ 179.7 (CS); 144.4 (CN); 134.5, 129.7, 129.6, 129.0, 128.5,
128.3, 127.8, 127.5 (CPh). IR (KBr) (νmax/cm-1): 3499, 3328, 3270,
3156, ν(NH), 1586, 1566, 1516, δ(NH2), 1593, ν(CdN), and 844,
ν(CS).
Recrystallization in ethanol gave orange crystals suitable for
X-ray crystallography.
square-planar geometries. In fact, a zinc complex of LH6
with a nitrate ion in the apical position of a square-based
pyramid has been previously proposed. In this article, we
report the direct synthesis and structural characterization of
new LH6 complexes with the same stoichiometry, in which
the deprotonate ligand shows a different coordination
behavior depending on the preference for a coordinated donor
atom and the geometry for the metal ion.
[CdC16H14N6S2]2, 2. The procedure was the same as for complex
1 but using Cd(NO3)2‚4H2O (96%). (Anal. Found: C, 40.89; H,
3.16; N, 17.68; S, 13.24. Calcd for CdC16H14N6S2: C, 41.16; H,
3.00; N, 18.01; S, 13.72.) FAB+ (m/z): 467.8 (Cd[LH4 + 1]+,
15%). MALDI-TOF (m/z): 468.1 ([CdLH4 + 1]+), 935.1 ([CdLH4]2
1
+ 1]+. H NMR (DMSO-d6): δ 7.5-6.8, m. 13C NMR (DMSO-
d6): δ 177.1 (CS); 146.4 (CN); 135.6, 129.7, 127.5, 127.4 (CPh).
113Cd NMR (DMF, 213 K): δ 229. 113Cd CP MAS NMR: δ 267.
IR (KBr) (νmax/cm-1): 3467, 3428, 3349, 3158, ν(NH); 1616, 1581,
1513, δ(NH2), 1596, ν(CdN), and 840, 813, ν(CS).
Recrystallization in a dimethylformamide/chloroform (9:1) solu-
tion gave orange crystals suitable for X-ray analysis.
Experimental Section
Physical Measurements. Microanalyses were carried out using
a Perkin-Elmer 2400 II CHNS/O elemental analyzer. IR spectra in
the 4000-400 cm-1 range were recorded as KBr pellets on a Jasco
FT/IR-410 spectrophotometer. 1H, 13C, and 113Cd NMR spectra were
recorded on a Bruker AMX-300 spectrophotometer using CDCl3,
DMSO-d6, and DMF/CDCl3 as solvents and TMS or 0.1 M aqueous
Cd(ClO)4 as references. The 113Cd CP MAS NMR spectrum was
obtained at 298 K in a Bruker Avance-400 spectrometer, using a
standard cross-polarization pulse sequence.33-36 The external
magnetic field was 9.4 T, and the sample was spun at 4-4.5 kHz
around an axis inclined 54° 44′ with respect to this field.
Spectrometer frequencies were set to 88.76 MHz. For the recorded
spectrum a contact time of 10 ms was used. The number of scans
ranged to 4000. Fast atom bombardment mass spectra were recorded
on a VG Auto Spec instrument using Cs as the fast atom and
m-nitrobenzyl alcohol (mNBA) as the matrix. MALDI-TOF-MS
spectra were recorded using a Bruker Reflex III mass spectrometer
equipped with a nitrogen laser emitting at 337 nm, using ditranol
as the matrix.
[NiC16H14N6S2], 3.38 A solution of 0.244 g (0.84 mmol) of Ni-
(NO3)2‚6H2O dissolved in 10 mL of ethanol was added over a
suspension of 0.300 g (0.84 mmol) of LH6 and 0.071 g (0.84 mmol)
of LiOH‚H2O in 40 mL of the same solvent. The mixture was stirred
for 3 h at room temperature. The reddish solid was filtered off,
washed with methanol, and vacuum-dried (87%). (Anal. Found:
C, 46.41; H, 3.42; N, 20.20; S, 15.46. Calcd for NiC16H14N6S2: C,
46.52; H, 3.39; N, 20.30; S, 15.53.) FAB+ (m/z): 412.9 ([NiLH4
1
+ 1]+, 30%). H NMR (DMSO-d6): δ 7.6 (4H NH2, s), 7.1-7.3
(10H Ph, m). 13C NMR (DMSO-d6): δ 179.7 (CS); 153.8 (CN);
131.6, 129.4, 128.8, 127.7 (CPh). IR (KBr): (νmax/cm-1): 3456,
3273, 3124, ν(NH), 1625, 1576, 1557, δ(NH2), 1615, ν(CdN), and
852, ν(CS).
Recrystallization in dimethylformamide gave red crystals suitable
for X-ray crystallography
All reagents and other solvents were obtained from standard
commercial sources and were used as received.
Crystallography. Crystals of compounds were mounted on a
glass fiber and transferred to a Bruker SMART 6K CCD area-
detector three-circle diffractometer with a MAC Science Co., Ltd.,
rotating anode (Cu KR radiation, λ ) 1.541 78 Å) generator
equipped with Goebel mirrors at settings of 50 kV and 110 mA.
X-ray data were collected at 296 K, with a combination of six runs
at different æ and 2θ angles, 3600 frames. The data were collected
using 0.3° wide ω scans (10 s/frame at 2θ ) 40° and 20 s/frame
at 2θ ) 100° for LH6, 30 s/frame at 2θ ) 40° and 60 s/frame at
2θ ) 100° for complex 1, 1 s/frame at 2θ ) 40° and 3 s/frame at
2θ ) 100° for complex 2, and 20 s/frame at 2θ ) 40° and 50
s/frame at 2θ ) 100° for complex 3), with crystal-to-detector
distance of 4.0 cm.
Synthesis. [C16H14N6S2], LH6. Benzil bis(thiosemicarbazone)
was prepared by following the procedure previously reported.37
FAB+ (m/z): 357 ([LH6 + 1]+, 100%), 714 ([(LH6)2 + 1]+, 25%).
1H NMR (DMSO-d6): δ 9.8 (2H, s), 8.6 (2H, s), 8.3 (2H, s), 7.7
(4H, m), 7.4 (6H, m). 1H NMR (CDCl3): δ 8.8 (2H, s), 7.6 (6H,m),
7.4 (4H, m), 6.6 (2H, s), 6.0 (2H, s). 13C NMR (DMSO-d6): δ
179.1 (CS), 140.5 (CN), 133.1, 130.1, 128.9, 126.8 (CPh). IR (KBr)
(νmax/cm-1): 3420, 3386, 3342, 3330, 3210, 3151, ν(NH), 1608,
δ(NH2), 1581, ν(CdN), and 848, ν(CS).
Slow evaporation of an ethanol/water solution (2:1) gave pale
yellow crystals suitable for X-ray analysis.
[ZnC16H14N6S2]∞, 1. A 0.249 g (0.84 mmol) amount of Zn-
(NO3)2‚6H2O dissolved in 10 mL of ethanol was added over a
suspension of 0.300 g (0.84 mmol) of LH6 and 0.071 g (0.84 mmol)
of LiOH‚H2O in 40 mL of the same solvent. The mixture was stirred
under reflux for 6 h. Then the orange solid was filtered off, washed
The substantial redundancy in data allows empirical absorption
corrections (SADABS)39 to be applied using multiple measurements
of symmetry-equivalent reflections (ratio of minimum to maximum
apparent transmission: 0.836211 for LH6, 0.862650 for complex
1, 0.352243 for complex 2, and 0.905221 for complex 3). The unit
cell parameters were obtained by full-matrix least-squares refine-
ments of 1239 reflections for LH6, 5227 reflections for complex 1,
8961 for complex 2, and 2969 for complex 3.
(33) Santos, R. A.; Gruff, E. S.; Koch, S. A.; Harbison, G. S. J. Am. Chem.
Soc. 1990, 112, 9257-9263.
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590.
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B. C.; Kurtz, D. M., Jr. J. Am. Chem. Soc. 1981, 103, 4400-4405.
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Puebla, E.; Ru´ız-Valero, C. Z. Naturforsch. 1994, 49b, 263-271.
(38) Can˜adas, M.; Lo´pez-Torres, E.; Mart´ınez-Arias, A.; Mendiola, M. A.;
Sevilla, M. T. Polyhedron 2000, 19, 2059-2068.
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1997-2001.
5224 Inorganic Chemistry, Vol. 43, No. 17, 2004

Zn, Cd, and Ni Benzil Bis(thiosemicarbazone)s
Table 1. Crystallographic Data for the Compounds
LH6
1
2
3
formula
M
C16H16N6S2
356.47
C16H14N6S2Zn
419.82
C22H28N8CdO2S2
613.04
C19H21N7NiOS2
486.26
cryst system
space group
a/Å
b/Å
triclinic
P1h
monoclinic
P21/n
12.7945(2)
9.0831(2)
14.9600(3)
90
97.0220(10)
90
1725.52(6)
4
1.616
4.339
856
1.051
3141
3141
0.0323, 0.0847
0.0384, 0.0886
monoclinic
C2/c
19.7587(3)
12.32270(10)
22.4943(3)
90
101.6190(10)
90
5364.69(12)
8
1.518
8.266
2496
1.050
16 449
4923
0.0409, 0.1205
0.0428, 0.1226
triclinic
P1h
9.6364(4)
9.9275(4)
10.2686
86.179(3)
70.671(3)
71.795(2)
879.84(7)
2
10.2602(4)
10.5285(5)
11.2091(5)
98.070(3)
108.113(3)
105.883(3)
1072.72(8)
2
c/Å
R/deg
â/deg
γ/deg
V/Å3
Z
Dc/Mg m-3
abs coeff/mm-1
F(000)
1.346
2.825
372
1.043
5685
2949
0.0427, 0.1111
0.0633, 0.1232
1.505
3.344
504
1.018
6968
3574
0.0359, 0.0920
0.0460, 0.0986
goodness of fit on F2
reflcns collcd
Indpndnt reflcns
final R1 and wR2 [I > 2σ(I)]
R indices (all data)
The raw intensity data frames were integrated with the SAINT40
program, which also applied corrections for Lorentz and polarization
effects.
spectrum of complex 1 only shows a very weak peak.
MALDI-TOF spectra of complexes 1 and 2 show a peak
corresponding to the empirical formula, and the spectrum
of the last complex shows an additional peak corresponding
to the molecular mass. The different behavior observed could
be explained probably because the Cd-S bond is stronger
than the Zn-N bond, and while the first one remains, the
second one is broken when the spectrum is carried out.
Complexes 1 and 2 are only soluble in strongly donor
solvents, as DMF and DMSO.
The software package SHELXTL41 version 6.10 was used for
space group determination, structure solution, and refinement. The
space group determination was based on a check of the Laue
symmetry and systematic absences and was confirmed using the
structure solution. The structure was solved by direct methods
(SHELXS-97),42 completed with difference Fourier syntheses, and
refined with full-matrix least squares using SHELXL-9743 minimiz-
ing ω(Fo2 - Fc2)2. Weighted R factors (Rw) and all goodness of fit
S are based on F2; conventional R factors (R) are based on F. All
non-hydrogen atoms were refined with anisotropic displacement
parameters. All scattering factors and anomalous dispersions factors
are contained in the SHELXTL 6.10 program library. The high
quality of the data set allowed that all hydrogen atoms were located
by difference maps and refined isotropically in all complexes, except
in the solvent molecules and aromatic hydrogens of complexes 2
and 3.
Crystallography. Crystallographic data of LH6 and its
complexes are summarized in Table 1.
Pale yellow crystals of LH6 suitable for X-ray diffraction
study were obtained by slow evaporation of an ethanol/water
mixture. The structure determination shows (Figure 1; Table
2) that the free ligand exists in the thione form (supported
by the presence of hydrazinic N-H and C-S distance of
1.67 Å, which is much shorter than a single C-S bond) and
corresponds to a structure where the two thiosemicarbazone
moieties are trans with respect to the single bond C(2)-
C(3) and the phenyls are in a perpendicular disposition, thus
minimizing the intramolecular interaction; both thiosemi-
carbazone branches are in a E disposition with respect to
the CN double bond. The X-ray data confirm the proposed
structure from a molecular modeling program (Hyperchem
version 3) previously published by us.44The distances and
bond angles of both thiosemicarbazone arms are very similar,
and the molecular conformation of the atoms and the
azomethine nitrogen atoms N(6) and N(3) is cis with respect
to the C(4)-N(5) and C(1)-N(2) bonds. The N-N distances
are shorter than 1.44 Å, accepted as typical for a single N-N
bond, and agree well with those of similar thiosemicarba-
zones.45 C-S bonds distances are intermediate between those
of single and double bond (1.82 and 1.56, respectively),46
showing the partial double bond character implied by the
CCDC reference numbers: 190456 for complex 1; 220143 for
LH6; 220144 for complex 2; 220145 for complex 3.
Results and Discussion
Complexes obtained present the same empirical formula
[MLH4].
Reactions between LH6 and Zn(NO3)2‚6H2O or Cd(NO3)2‚
4H2O depend on the working conditions; in the presence of
a basic medium they give, with a quantitative yield,
complexes 1 and 2, respectively. In both of them, the ligand
acts as dianion by the loss of the hydrogen of the secondary
amine in contrast with the complexes previously prepared
in absence of this medium.32 The nickel complex 3 was
obtained under the same conditions as the other and in the
absence of basic medium.38 FAB+ mass spectra of com-
plexes 2 and 3 confirm the empirical formula; however the
(40) Sheldrick, G. M. SAINT+NT Ver.6.04. SAX Area-Detector Integration
Program; Bruker AXS: Madison, WI, 1997-2001.
(41) Bruker AXS SHELXTL Version 6.10. Structure Determination Package;
Bruker AXS: Madison, WI, 2000.
(42) Sheldrick, G. M. SHELXS-97, Program for Structure Solution. Acta
Crystallogr., Sect. A 1990, 46, 467-473.
(43) SHELXL-97, Program for Crystal Structure Refinement; Universita¨t
Go¨ttingen: Go¨ttingen, Germany, 1997.
(44) Arquero, A.; Can˜adas, M.; Mart´ınez-Ripoll, M.; Mendiola, M. A.;
Rodr´ıguez, A. Tetrahedron 1998, 54, 11271-11284.
(45) Bermejo, E.; Castin˜eiras, A.; Dom´ınguez, R.; Carballo, R.; Maiche-
Mo¨ssmer C.; Stra¨hle, J.; West, D. X. Z. Anorg. Allg. Chem. 1999,
625, 961-968 and references therein.
Inorganic Chemistry, Vol. 43, No. 17, 2004 5225

Lo´pez-Torres et al.
Figure 1. Molecular structure of LH6. Thermal ellipsoids are shown at 50% probability.
Table 2. Selected Bond Distances (Å) and Angles (deg) for LH6
through an extended network of intermolecular hydrogen
bonds involving the amine nitrogen atoms N(1) and N(4)
and the sulfur atoms S(1) and S(2) (Figure 2; Table 3).
Orange crystals of [ZnLH4]∞, 1, suitable for X-ray dif-
fraction study were obtained by recrystallization in ethanol.
Crystallographic data of complex 1 indicate that the Zn(II)
ion is pentacoordinated in a distorted square-based pyramidal
structure (Figure 3) and both thiosemicarbazone arms are in
E disposition. Selected bond distances and angles are
summarized in Table 4. The value of the parameter τ defined
by Addison et al.47 is 0.04 (τ ) 0 for a regular square-based
pyramid). The coordination sphere of the zinc atom is formed
by two sulfurs, two imine nitrogen atoms, and a nitrogen
atom from a terminal amine group belonging to another
ligand. To the best of our knowledge, this is the first time
that a bis(thiosemicarbazonate) complex with this behavior
has been crystallographically characterized. The N2S2 donor
atoms of the tetradentate ligand define the base with a
maximum deviation of 0.113 Å for N(5). The axial site is
occupied by a NH2 group. The zinc atom is displaced out of
the basal plane by 0.412 Å toward the atom at the apex of
the pyramid. The angle formed by the Zn-N(2A) bond with
the normal to the basal plane is 10°. The pseudomacrocyclic
C(1)-N(1)
C(1)-N(2)
C(1)-S(1)
C(2)-N(3)
C(2)-C(3)
C(2)-C(5)
C(3)-N(6)
1.305(3)
1.369(3)
1.667(3)
1.298(3)
1.478(3)
1.490(3)
1.294(3)
C(3)-C(11)
C(4)-N(4)
C(4)-N(5)
C(4)-S(2)
N(2)-N(3)
N(5)-N(6)
1.490(3)
1.306(4)
1.367(3)
1.668(3)
1.361(3)
1.362(3)
N(1)-C(1)-N(2)
N(1)-C(1)-S(1)
N(2)-C(1)-S(1)
N(3)-C(2)-C(3)
N(3)-C(2)-C(5)
C(3)-C(2)-C(5)
N(6)-C(3)-C(2)
N(6)-C(3)-C(11)
C(2)-C(3)-C(11)
N(4)-C(4)-N(5)
115.8(2)
125.6(2)
118.68(19)
114.0(2)
125.0(2)
121.0(2)
114.2(2)
125.6(2)
120.2(2)
115.7(3)
N(4)-C(4)-S(2)
N(5)-C(4)-S(2)
C(6)-C(5)-C(2)
C(10)-C(5)-C(2)
C(16)-C(11)-C(3)
C(12)-C(11)-C(3)
N(3)-N(2)-C(1)
C(2)-N(3)-N(2)
N(6)-N(5)-C(4)
C(3)-N(6)-N(5)
126.0(2)
118.3(2)
120.4(2)
121.3(2)
120.5(2)
121.1(2)
119.0(2)
118.7(2)
119.1(2)
118.9(2)
canonical structures usually considered for thiosemicarba-
zones. Azomethine bond lengths are likewise short enough
to imply a partial double bond. Formation of complexes, in
which the ligand acts as a N2S2 chelate, takes place via three
180° rotations about C(2)-C(3), C(1)-N(2), and C(4)-N(5)
bonds. The molecules are held together in the crystal packing
(46) Sutton, E. Tables of Interatomic Distances and Configuration in
Molecules and Ions (Supplement); The Chemical Society: London,
1965.
(47) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G.
C. J. Chem. Soc., Dalton Trans. 1984, 1349-1356.
5226 Inorganic Chemistry, Vol. 43, No. 17, 2004

Zn, Cd, and Ni Benzil Bis(thiosemicarbazone)s
Figure 2. A plot including the hydrogen bonds in LH6.
Table 3. Hydrogen bonds for LH6 (Å, deg)
Table 4. Selected Bond Distances (Å) and Angles (deg) for 1a
D-H‚‚‚Aa
N(4)-H(4B)‚‚‚S(2)#1
N(4)-H(4B)‚‚‚S(1)#2
N(1)-H(1B)‚‚‚S(1)#3
d(D-H)
d(H‚‚‚A)
d(D‚‚‚A)
(DHA)
Zn(1)-N(5)
Zn(1)-N(4)
Zn(1)-N(2)#1
Zn(1)-S(1)
Zn(1)-S(2)
S(1)-C(1)
S(2)-C(4)
C(1)-N(3)
C(1)-N(1)
C(2)-N(4)
C(2)-C(5)
C(2)-C(3)
2.097(2)
2.1393(19)
2.170(2)
2.3318(7)
2.3621(7)
1.730(3)
1.732(2)
1.334(3)
1.339(3)
1.301(3)
1.485(3)
1.494(3)
C(3)-N(5)
C(3)-C(11)
C(4)-N(6)
C(4)-N(2)
N(1)-H(1A)
N(1)-H(1B)
N(2)-Zn(1)#2
N(2)-H(2A)
N(2)-H(2B)
N(3)-N(4)
N(5)-N(6)
1.293(3)
1.482(3)
1.299(3)
1.401(3)
0.80(3)
0.80(3)
2.170(2)
0.64(3)
0.83(4)
0.81(3)
0.87(4)
2.57(4)
3.01(3)
2.48(4)
3.392(3)
3.531(3)
3.340(3)
172(3)
125(3)
171(3)
a Symmetry transformations used to generate equivalent atoms: (#1) -x
+ 1, -y + 2, -z + 1; (#2) x - 1, y, z; (#3) -x + 3, -y + 2, -z + 2.
0.76(3)
1.369(3)
1.376(3)
N(5)-Zn(1)-N(4)
N(5)-Zn(1)-N(2)#1
74.07(8)
N(6)-C(4)-N(2)
114.1(2)
129.62(19)
116.22(19)
118(2)
119(2)
122(3)
99.03(10) N(6)-C(4)-S(2)
N(4)-Zn(1)-N(2)#1 101.62(8)
N(2)-C(4)-S(2)
N(5)-Zn(1)-S(1)
N(4)-Zn(1)-S(1)
150.84(6)
81.16(6)
C(1)-N(1)-H(1A)
C(1)-N(1)-H(1B)
H(1A)-N(1)-H(1B)
C(4)-N(2)-Zn(1)#2
C(4)-N(2)-H(2A)
N(2)#1-Zn(1)-S(1) 100.83(8)
N(5)-Zn(1)-S(2)
N(4)-Zn(1)-S(2)
81.70(6)
148.26(6)
116.77(17)
109(3)
N(2)#1-Zn(1)-S(2) 102.17(6)
Zn(1)#2-N(2)-H(2A) 110(3)
S(1)-Zn(1)-S(2)
C(1)-S(1)-Zn(1)
C(4)-S(2)-Zn(1)
N(3)-C(1)-N(1)
N(3)-C(1)-S(1)
N(1)-C(1)-S(1)
N(4)-C(2)-C(5)
N(4)-C(2)-C(3)
C(5)-C(2)-C(3)
N(5)-C(3)-C(11)
N(5)-C(3)-C(2)
C(11)-C(3)-C(2)
114.34(3)
94.86(9)
93.71(8)
115.0(2)
C(4)-N(2)-H(2B)
Zn(1)#2-N(2)-H(2B)
H(2A)-N(2)-H(2B)
C(1)-N(3)-N(4)
112(3)
98(3)
110(4)
111.76(19)
121.51(19)
117.40(16)
119.39(15)
119.3(2)
119.57(16)
121.08(15)
112.2(2)
128.17(19) C(2)-N(4)-N(3)
116.9(2)
124.2(2)
114.1(2)
121.6(2)
123.8(2)
113.9(2)
122.2(2)
C(2)-N(4)-Zn(1)
N(3)-N(4)-Zn(1)
C(3)-N(5)-N(6)
C(3)-N(5)-Zn(1)
N(6)-N(5)-Zn(1)
C(4)-N(6)-N(5)
a Symmetry transformations used to generate equivalent atoms: (#1) -x
+ 1/2, y - 1/2, -z + 3/2; (#2) -x + 1/2, y + 1/2, -z + 3/2.
Figure 3. Molecular structure of [ZnC16H14N6S2]∞, 1, with the atom
labeling scheme. Thermal ellipsoids are shown at 40% probability.
1.334(3) and 1.299(3) Å for the C(4)-N(6) and C(1)-N(3)
bonds with respect to the free ligand [1.367(3) Å]. It can be
pointed out that, owing to the dideprotonation, the C-S
double bond character is smaller than in the complex [Cd-
(NO3)2LH6].32 The bond N(2)-C(4) is larger than N(1)-
C(1) because the N(2) is bonded to the zinc and then the
delocalization is smaller than in the other amine group. The
bond distance between the zinc atom and the amine nitrogen
from the other ligand is slightly larger than the other Zn-N
bonds, but it is close to those observed in some thiosemi-
carbazide complexes.48 Furthermore the bond angles in the
bis(thiosemicarbazone) ligand are also compatible with the
electronic delocalization. Remaining bond distances and
coordination mode of the ligand affords three five-member
chelate rings. The phenyl rings C(5)-C(10) and C(11)-
C(16) form with respect to the basal plane dihedral angles
of 54.81 and 52.64°, respectively. The angle between phenyl
rings is 57.74°. In accordance with the symmetry of the
ligand, bond distances and angles in both thiosemicarbazone
moieties are similar. Bond lengths agree with a considerable
electronic delocalization through the thiosemicarbazone
backbone, enhanced upon deprotonation. Thus, the thione
bond distances of ca. 1.73 Å are intermediate between a
theoretical C-S single and double bond and longer than in
the free ligand, as occurs with the N-N bonds (1.37 vs. 1.44
Å calculated for a single N-N). The different behavior of
two thiosemicarbazone arms reflects on the values of
(48) Babb, J. E. V.; Burrows, A. D.; Harrington, R. W.; Mahon, M. F.
Polyhedron 2003, 22, 673-686 and references therein
Inorganic Chemistry, Vol. 43, No. 17, 2004 5227

Lo´pez-Torres et al.
Table 5. Selected Bond Distances (Å) and Angles (deg) for
[CdC16H14N6S2]2‚2DMFa
Cd(1)-N(4)
Cd(1)-N(3)
Cd(1)-S(1)
Cd(1)-S(2)#1
Cd(1)-S(2)
S(1)-C(1)
S(2)-C(16)
S(2)-Cd(1)#1
C(1)-N(2)
C(1)-N(1)
2.308(3)
C(2)-N(3)
C(2)-C(3)
C(2)-C(9)
C(9)-N(4)
C(9)-C(10)
C(16)-N(5)#1
C(16)-N(6)
N(2)-N(3)
N(4)-N(5)
N(5)-C(16)#1
1.290(4)
1.488(4)
1.493(4)
1.295(4)
1.491(4)
1.319(5)
1.327(5)
1.375(4)
1.368(4)
1.319(5)
2.329(3)
2.4973(9)
2.6128(9)
2.6337(9)
1.745(4)
1.789(4)
2.6128(9)
1.318(5)
1.338(5)
Figure 4. Formation of a 1D chain along the b direction based on the
ZnC16H14N6S2 building unit.
N(4)-Cd(1)-N(3)
N(4)-Cd(1)-S(1)
N(3)-Cd(1)-S(1)
N(4)-Cd(1)-S(2)#1
N(3)-Cd(1)-S(2)#1
S(1)-Cd(1)-S(2)#1
N(4)-Cd(1)-S(2)
N(3)-Cd(1)-S(2)
S(1)-Cd(1)-S(2)
S(2)#1-Cd(1)-S(2)
C(1)-S(1)-Cd(1)
C(16)-S(2)-Cd(1)#1
C(16)-S(2)-Cd(1)
Cd(1)#1-S(2)-Cd(1)
N(2)-C(1)-N(1)
N(2)-C(1)-S(1)
69.44(9)
140.18(8)
75.32(7)
N(3)-C(2)-C(3)
N(3)-C(2)-C(9)
C(3)-C(2)-C(9)
N(4)-C(9)-C(10)
N(4)-C(9)-C(2)
C(10)-C(9)-C(2)
124.3(3)
116.3(3)
119.4(3)
123.9(3)
116.4(3)
119.6(3)
74.17(7)
136.35(7)
124.98(3)
104.39(8)
121.81(8)
109.67(4)
89.74(3)
96.93(11) C(2)-N(3)-N(2)
93.80(11) C(2)-N(3)-Cd(1)
103.23(13) N(2)-N(3)-Cd(1)
87.18(3)
116.1(4)
129.1(3)
114.8(3)
N(5)#1-C(16)-N(6) 117.3(4)
N(5)#1-C(16)-S(2)
N(6)-C(16)-S(2)
C(1)-N(2)-N(3)
127.0(3)
115.5(3)
112.7(3)
120.0(3)
118.1(2)
121.2(2)
118.7(3)
118.5(2)
122.0(2)
C(9)-N(4)-N(5)
C(9)-N(4)-Cd(1)
N(5)-N(4)-Cd(1)
N(1)-C(1)-S(1)
C(16)#1-N(5)-N(4) 114.5(3)
Figure 5. Molecular structure of [CdC16H14N6S2]2‚2DMF with atom
labeling scheme. Thermal ellipsoids are shown at 50% probability. Hydrogen
atoms are omitted for clarity.
a Symmetry transformations used to generate equivalent atoms: (#1) -x,
y, -z + 1/2.
angles are similar to those found in related complexes and
do not deserve further comments.
The structure of [ZnLH4]∞ is made up of [ZnLH4] units,
which are connected by a NH2 group acting as bridge
between two units, leading infinite 1D chains running along
the b direction (Figure 4).
distance corresponding to the bridging sulfur is larger
[1.788(4) Å] and closer to the value expected for a C-S
single bond (1.82 Å), as could be expected. The Cd-N bond
distances are similar [2.308(3) and 2.329(3) Å], but Cd-S
distances involving the bridging sulfur [2.6337(9) and
2.6129(9) Å] are larger than the remaining Cd-S distance
[2.4972(9) Å]. The Cd-N bond distances are shorter than
in the complex [Cd(NO3)2LH6],32 and there is one Cd-S
bond distance shorter and one larger (with the bridging
sulfur), as expected for the behavior of the ligand. The
coordination mode of the ligand affords six five-member and
one four-member chelate rings. There is an extended network
of intermolecular hydrogen bonds with the DMF molecules
and between the dinuclear units (Figure 6; Table 6).
Red crystals of 3 were obtained from a dimethylformamide
solution. The crystal structure consists of two units of
[NiLH4] and two dimethylformamide molecules, held to-
gether in the crystal packing by hydrogen bonds. A perspec-
tive view of [NiLH4]‚2DMF with the atom-labeling scheme
is given in Figure 7, and selected bond angles and distances
are given in Table 7. Crystallographic data of complex
confirm the geometry predicted from spectroscopic data,38
showing that the Ni(II) ion is tetracoordinate in a planar
disposition. The coordination sphere of the nickel atom is
formed by two sulfur and two imine nitrogen atoms as
expected for this ligand. Bond distances Ni-L are in the
range found for this kind of complex. Bond distances and
angles are in accordance with electronic delocalization in
the ligand. They are similar to those of complex 1, although
the C-S bond is slightly longer. The environment of the
nickel ion is planar with a maximum deviation of 0.015 Å
for N(1). Finally, the molecules are held together in the
Orange crystals of 2 were obtained in a dimethylforma-
mide/chloroform solution. Discrete [CdLH4] entities form the
crystal structure of the complex, linked through one sulfur
atom of each thiosemicarbazonate ligand, which leads to the
dinuclear centrosymmetric [CdLH4]2 species, with two
crystallization molecules of DMF. The molecular structure
of [CdLH4]2‚2DMF is shown in Figure 5. Selected inter-
atomic dimensions are given in Table 5. The cadmium(II)
ions are five-coordinate with four positions occupied by two
imine nitrogen and two sulfur atoms from the thiosemicar-
bazonate ligand and the five position occupied by the sulfur
atom of the adjacent [CdLH4] entity. The distortion of the
coordination polyhedron from square-pyramidal (τ ) 0) and
trigonal-bipyramidal (τ ) 1) topologies has been analyzed.47
The τ value obtained was 0.06, which clearly indicates that
the environment of the cadmium(II) ion is close to a square-
pyramidal geometry. The two cadmium atoms are separated
by 3.613 Å, and the bridging sulfur atoms, by 3.703 Å. The
mean deviation of N(3), N(4), S(1), and S(2) from the least-
squares plane through the four is 0.061 Å for N(3) and N(4),
and the cadmium atom lies 0.619 Å above this plane. The
thiosemicarbazone backbone is pseudoplanar, with a maxi-
mum deviation of 0.191 Å for S(2A), the bridging sulfur.
Bond distances and angles are compatible with electronic
delocalization. Within [CdLH4], bond distances of both
thiosemicarbazonate branches are quite similar (and similar
to complex 1), except those of C-S bonds, where the
5228 Inorganic Chemistry, Vol. 43, No. 17, 2004

Zn, Cd, and Ni Benzil Bis(thiosemicarbazone)s
Figure 6. Plot of [CdC16H14N6S2]2‚2DMF including hydrogen bonds with
the DMF molecules. Phenyl rings are omitted for clarity.
Table 6. Hydrogen bonds for [CdC16H14N6S2]2‚2DMF (Å, deg)a
D-H‚‚‚A
d(D-H)
d(H‚‚‚A)
d(D‚‚‚A)
(DHA)
N(6)-H(6B)‚‚‚O(2)
N(6)-H(6A)‚‚‚O(1)
N(1)-(1A)‚‚‚N(2)#2
0.68
0.97
0.74
2.21
2.02
2.39
2.859
2.948
3.125(5)
162
160
167
a Symmetry transformations used to generate equivalent atoms: (#2) -x
+ 1/2, -y + 3/2, -z + 1.
Figure 7. Molecular structure of [NiC16H14N6S2]‚2DMF with the atom
crystal packing through an extended network of intermo-
lecular hydrogen bonds involving the amino groups, S(2)
and N(5) atoms, and the oxygen atom from the DMF
molecules (see Figure 8; Table 8).
labeling scheme. Thermal ellipsoids are shown at 40% probability.
Table 7. Selected Bond Distances (Å) and Angles (deg) for
[NiC16H14N6S2]‚2DMF
Spectroscopy. The Experimental Section lists the main
IR bands of the ligand and its complexes. In the complexes
the number of bands corresponding to ν(N-H) vibrations
have decreased due to deprotonation and the others appear
at higher frequencies probably due to that the intermolecular
hydrogen bonding has decreased. In the margin of the
deformation modes of the primary amine groups, a different
behavior is observed; the spectrum of nickel complex 3
shows two bands, and the spectrum of complex 1 presents
double number of bands suggesting a different behavior for
the two NH2 groups. The ν(CdN) band are shifted to higher
frequencies in all complexes, a clear sign of coordination
via the azomethine nitrogen atom.
The values of the chemical shifts of the amine hydrogen
atoms in the 1H NMR spectrum of LH6 depend on the donor
character of the solvent. This fact is related to the grade of
rupture of the intermolecular hydrogen bonds present in the
solid state. 1H NMR spectra of complexes 1 and 2 are very
similar. In both of them the signal of hydrogen atoms of the
secondary amine has disappeared and the signal correspond-
ing to the terminal amine hydrogen atoms is shifted to high
field, and it is inside the multiplet of the aromatic hydrogen
atoms. In the spectrum of complex 3 the signal of the H(NH)
has also disappeared, but a signal corresponding to the
hydrogen of the terminal amine group is observed at higher
C(1)-N(3)
C(1)-N(2)
C(1)-S(1)
C(2)-N(1)
C(2)-C(3)
C(2)-C(9)
C(9)-N(4)
C(10)-C(9)
C(16)-N(5)
1.341(3)
1.320(3)
1.744(3)
1.307(3)
1.475(3)
1.474(3)
1.308(3)
1.474(3)
1.328(3)
C(16)-N(6)
C(16)-S(2)
N(1)-N(2)
N(1)-Ni(1)
N(4)-N(5)
N(4)-Ni(1)
Ni(1)-S(1)
Ni(1)-S(2)
1.330(3)
1.745(3)
1.371(3)
1.862(2)
1.372(3)
1.861(2)
2.1462(3)
2.1572(3)
N(3)-C(1)-N(2)
N(3)-C(1)-S(1)
N(2)-C(1)-S(1)
N(1)-C(2)-C(9)
N(1)-C(2)-C(3)
C(2)-C(9)-C(10)
C(9)-C(2)-C(3)
N(4)-C(9)-C(2)
N(4)-C(9)-C(10)
N(5)-C(16)-N(6)
N(5)-C(16)-S(2)
N(6)-C(16)-S(2)
C(2)-N(1)-N(2)
C(2)-N(1)-Ni(1)
117.9(2)
117.3(2)
124.81(19)
113.1(2)
124.1(2)
123.2(2)
122.7(2)
111.9(2)
125.0(2)
117.3(2)
124.48(19)
118.3(2)
120.7(2)
115.43(17)
N(2)-N(1)-Ni(1)
C(1)-N(2)-N(1)
C(9)-N(4)-N(5)
C(9)-N(4)-Ni(1)
N(5)-N(4)-Ni(1)
C(16)-N(5)-N(4)
N(4)-Ni(1)-N(1)
N(4)-Ni(1)-S(1)
N(1)-Ni(1)-S(1)
N(4)-Ni(1)-S(2)
N(1)-Ni(1)-S(2)
S(1)-Ni(1)-S(2)
C(1)-S(1)-Ni(1)
C(16)-S(2)-Ni(1)
123.88(16)
109.4(2)
120.5(2)
116.08(17)
123.42(16)
110.0(2)
83.31(9)
170.68(6)
87.39(7)
87.62(6)
170.87(7)
101.68(3)
94.26(9)
94.08(8)
field than in the free ligand. These facts agree with that, in
all complexes, the ligand is dideprotonated.
13C NMR spectra of complexes 2 and 3 show four signals
corresponding to phenyl carbon atoms. This fact indicates
that complex 2 is symmetric in solution, so the sulfur bridge
must be broken when the complex is dissolved in DMSO.
Inorganic Chemistry, Vol. 43, No. 17, 2004 5229

Lo´pez-Torres et al.
increasing the coordination number tends to give more
shielded values.31 Taking into account both factors and for
comparison with the complex [Cd(NO3)2LH6]32 and other
compounds found in the literature, the value of the 113Cd
chemical shift in solution and in the solid state is in
agreement with a N2S3 environment for cadmium ions.
Conclusions
We present the crystal structure of benzil bis(thiosemi-
carbazone), which confirms the structure previously proposed
by us.44 The structure shows a trans disposition of the
thiosemicarbazone moieties, which changes to cis to form a
N2S2 chelate in all complexes.
The results presented in this work are a good example to
prove the importance of the working conditions and the
coordination preferences for a metal ion in the structural
characteristic of the complexes derived from a particular
ligand. The presence of a basic medium decides the anionic
behavior of benzil bis(thiosemicarbazone) in zinc and
cadmium complexes, whereas in the case of nickel it is
always the most favorable situation in all conditions. More
important is the preference of the coordination number of
the metal ion. The N2S2 planar disposition provided by LH6
is adequate to the nickel ion yielding a planar structure for
this complex. However, it forces the zinc and cadmium
complexes (both show the same spectroscopic characteristics
and are usually isostructural) to adopt an alternative structure,
in the zinc one a monodimensional chain through a NH2
group in a polymeric structure, observed for the first time
in a bisthiosemicarbazone ligand, and a dinuclear complex
with bridging sulfur atoms for the cadmium derivative, both
with pentacoordinate geometry. To explain this different
behavior, one should note that since cadmium(II) is a soft
ion, it prefers to bond to sulfur instead of to nitrogen atoms,
so the polymeric structure formed in complex 1 through an
amine nitrogen atom is less favorable, and bonding to sulfur
is preferred. It must be borne in mind that the two complexes
are not strictly comparable: the Cd(II) derivative is a DMF
solvate in which the solvent molecules interact with the NH2
group, which must make the coordination of this group more
difficult, so the formation of the polymeric structure should
be less favorable than the dimeric one. The combination of
both factors, geometry and softness of the metal ion, would
permit one to design selective routes to get novel architec-
tures.
Figure 8. Plot of complex [NiC16H14N6S2]‚2DMF including the hydrogen
bonds with the DMF molecules.
Table 8. Hydrogen bonds for [NiC16H14N6S2]‚2DMF (Å, deg)a
D-H‚‚‚A
d(D-H)
d(H‚‚‚A)
d(D‚‚‚A)
(DHA)
N(6)-H(6B)‚‚‚N(5)#1
N(3)-H(3B)‚‚‚O(1)#2
N(3)-H(3A)‚‚‚S(2 )#3
0.84
0.87
0.79
2.17
2.01
3.03
3.000
2.867
3.735
172
167
150
a Symmetry transformations used to generate equivalent atoms: (#1) -x
- 1, -y, -z + 1; (#2) -x + 1, -y, -z + 1; (#3) -x, -y + 1, -z + 2.
For complex 3 the number of signals agrees with the structure
of the complex. In complex 1 the number of signals indicates
asymmetry in the phenyl groups, induced by the nonsym-
metric coordination mode of LH4, as the crystal structure
shows. From the signals attributed to the carbon bonded to
the sulfur and the nitrogen atoms can be deduced that the
imine and thio groups are bonded to the metal atom in all
complexes.
The 113Cd CP MAS NMR spectrum of complex 2 shows
a signal at 267 ppm, which is broaden probably due to some
heterogeneity in the solid state. This value is within the range
expected for cadmium five-coordinate complexes.49 The
113Cd NMR of complex 2 in DMF at 213 K shows a signal
at 229 ppm, which is in agreement with the value obtained
in the solid state but more shielded, which could indicate
the partial substitution of the atoms bonded to the cadmium
by solvent molecules. Sulfur ligands are most strongly
deshielding, while nitrogen and oxygen donor ligands have
a weaker deshielding effect on the Cd(II) ion.50 Moreover,
Acknowledgment. We thank the Direccio´n General de
Investigacio´n, Ministerio de Ciencia y Tecnolog´ıa of Spain
(Project BQU2001-0151), for financial support.
Supporting Information Available: X-ray crystallographic data
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
(49) Summers, M. F. Coord. Chem. ReV. 1988, 86, 43-134.
(50) Casas, J. S.; Castan˜o, M. V.; Castellano, E. E.; Garc´ıa-Tasende, M.
S.; Sa´nchez, A.; Sanjua´n, L. M.; Sordo, J. Eur. J. Inorg. Chem. 2000,
83-89 and references therein.
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5230 Inorganic Chemistry, Vol. 43, No. 17, 2004