Complexes of a triazine-3-thione ligand with divalent metals: Crystal structure of [CdL2DMF]2·2DMF·1/4H 2O

Article abstract of DOI:10.1016/j.poly.2005.03.093

The synthesis and characterization of Cd(II), Zn(II), Pb(II), Co(III) and Ni(II) complexes of 5-methoxy-5,6-diphenyl-4,5-dihydro-2H-[1,2,4]triazine-3- thione LH₂OCH₃ are reported. The stoichiometry of the complexes was found to be 1:2 except for cobalt complex 4 where the ratio is 1:3. In all complexes the triazine is deprotonated and acts at least as a NS bidentate ligand. The complexes have been characterised by microanalysis, mass spectrometry, IR, multinuclear (¹H, ¹³C and ¹¹³Cd) NMR, ¹³C CP/MAS NMR and magnetic susceptibility. In addition, the structure of the complex [Cd(DMF)L₂] ₂·2DMF·1/4H₂O (1a), has been determined by X-ray diffraction. Crystallographic data show that the complex consists of a dinuclear structure, in which the ligands act as bidentate NS donors and with two of the four ligands acting as a bridge between the metal ions via the sulfur atom. According to the spectroscopic data, the same disposition is proposed for complexes 2 and 3. Complex 4 is an low spin octahedral monomeric structure with the ligand acting as a bidentate NS donor and where the metal has been oxidised to Co(III). In complex 5 the Ni(II) ion is in a square planar N ₂S₂ disposition, formed by two ligands. The redox behaviour of the cadmium and cobalt complexes was explored by cyclic voltammetry and shows metal-centred processes.

Full text of DOI:10.1016/j.poly.2005.03.093

Polyhedron 24 (2005) 1435–1444
www.elsevier.com/locate/poly
Complexes of a triazine-3-thione ligand with divalent metals
Crystal structure of [CdL2DMF]2 Æ 2DMF Æ 1/4H2O
a
*
´
Elena Lopez-Torres , M . Antonia Mendiola
´ ´ ´
Departamento de Quımica Inorganica, Universidad Autonoma de Madrid, Ciudad Universitaria de Cantoblanco, 28049 Madrid, Spain
Received 26 January 2005; accepted 18 March 2005
Available online 3 June 2005
Abstract
The synthesis and characterization of Cd(II), Zn(II), Pb(II), Co(III) and Ni(II) complexes of 5-methoxy-5,6-diphenyl-4,5-dihy-
dro-2H-[1,2,4]triazine-3-thione LH2OCH3 are reported. The stoichiometry of the complexes was found to be 1:2 except for cobalt
complex 4 where the ratio is 1:3. In all complexes the triazine is deprotonated and acts at least as a NS bidentate ligand. The com-
plexes have been characterised by microanalysis, mass spectrometry, IR, multinuclear (1H, 13C and 113Cd) NMR, 13C CP/MAS
NMR and magnetic susceptibility. In addition, the structure of the complex [Cd(DMF)L2]2 Æ 2DMF Æ 1/4H2O (1a), has been deter-
mined by X-ray diffraction. Crystallographic data show that the complex consists of a dinuclear structure, in which the ligands act as
bidentate NS donors and with two of the four ligands acting as a bridge between the metal ions via the sulfur atom. According to the
spectroscopic data, the same disposition is proposed for complexes 2 and 3. Complex 4 is an low spin octahedral monomeric struc-
ture with the ligand acting as a bidentate NS donor and where the metal has been oxidised to Co(III). In complex 5 the Ni(II) ion is
in a square planar N2S2 disposition, formed by two ligands. The redox behaviour of the cadmium and cobalt complexes was
explored by cyclic voltammetry and shows metal-centred processes.
Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: Triazine; Metal complexes; Crystal structure; Cyclic voltammetry
1. Introduction
agents, in electrochemistry as multi-step redox systems
and as pesticide or herbicide components in agriculture.
In the last few years, there has been a growing interest in
these compounds, which have been used, for example, as
templates in multidimensional crystal engineering
involving metal complexes for producing nanometer
sized oligonuclear coordination compounds, as scaffolds
in combinatorial chemistry, as well as new building
blocks in peptidomimetics and as anticancer agents
[7,8]. Therefore the synthesis of metallic compounds
with triazines derived from thiosemicarbazones is an
interesting topic to pursue.
Interest in Schiff base macroligands based on thiose-
micarbazones and their metallic derivatives has arisen in
recent decades, due to their wide range of pharmacolog-
ical properties, which confers numerous applications,
for example as antibacterial, antiviral and anticancer
agents [1–4]. Moreover they can be used in the prepara-
tion of potentiometric ion-selective electrodes (ISE), to
detect and if possible to remove toxic metals [5,6]. In
addition, triazine derivatives have traditionally found
applications in analytical chemistry as complexation
Due to the electronic delocalisation, which is en-
hanced upon deprotonation, TSC ligands are very versa-
tile. This fact, together with the presence of different
types of donor atoms, makes several coordination
modes possible [9,10]. So that, depending on the metal
*
Corresponding author. Tel.: +349 1497 4844; fax: +349 1497 4833.
´
E-mail addresses: elena.lopez@uam.es (E. Lopez-Torres), antonia.
mendiola@uam.es (Ma.A. Mendiola).
0277-5387/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.03.093

a
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E. Lopez-Torres, M . A. Mendiola / Polyhedron 24 (2005) 1435–1444
1436
coordination preferences, the ligand can show different
coordination behaviour.
2. Experimental
Although Zn(II) has a preference for tetrahedral
coordination [11], there are many complexes with coor-
dination numbers 5 and 6, which in many cases are in-
duced by conformational requirements of the ligands.
The same situation is found in the case of Cd(II), but
with a greater preference for high coordination numbers
than zinc (II) [10,12]. Pb(II) can adopt many different
geometries in its complexes, allowing a degree of toler-
ance for ligand configuration which is not seen, for
example, in d-block elements. Coupled with the ability
to bind well both hard and soft donor atoms, these
properties make Pb(II) an interesting metal to study,
forming as it often does complexes different from those
that might be conventionally expected. In the case of
Ni(II), square planar complexes with strong field ligands
are very stable, although octahedral complexes are also
common. When cobalt (II) complexes are synthesised,
oxidation to Co(III) is possible, specially in alkali med-
ium in the presence of N-donor ligands. Co(II) com-
plexes can adopt different geometries, while Co(III)
complexes are virtually all low-spin and octahedral.
In previous works we have reported the synthesis and
characterization of some coordination compounds with
ligands derived from benzil and thiosemicarbazide: an
open chain thiosemicarbazone, which shows the versa-
tile chelating behaviour of TSC ligands [13], as well as
the title ligand with some organotin (IV) derivatives.
In this case complexes with 1:1 and 1:2 stoichiometries
can be obtained, depending on the counter ion, in which
the triazine acts always as a NS chelate. In the 1:2 com-
plexes the ligands occupy the equatorial positions in a
distorted octahedral arrangement [14].
2.1. Physical measurements
Microanalyses were carried out using a Perkin–El-
mer 2400 II CHNS/O Elemental Analyser. IR Spectra
in the 4000–400 cmꢀ1 range were recorded as KBr pel-
lets on a Jasco FT/IR-410 spectrophotometer. H, 13C
1
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 aque-
ous Cd(ClO)4 as references. 13C CP/MAS NMR spec-
tra were obtained at 298 K on a Bruker avance-400
spectrometer, using a standard cross-polarisation pulse
sequence [15–18]. The external magnetic field was 9.4
T, and the sample was spun at 4–4.5 kHz around an
axis inclined 54°440 with respect to this field. Spectrom-
eter frequencies were set to 100.63 MHz. For the re-
corded spectra a contact time of 1 ms was used. The
number of scans were about 4000. The analysis was
done with the WINFIT program. In this program the
principal values of the chemical shift anisotropy tensor
were determined from the intensity of the sidebands
with the Herzfeld and Bergerꢀs method [19]. Fast atom
bombardment (FAB) mass spectra were recorded on a
VG Auto Spec instrument using Cs as the fast atom
and m-nitrobenzilalcohol (mNBA) as the matrix. Ma-
trix assisted laser desorption ionisation-time of flight
(MALDI-TOF) mass spectra were recorded using a
Bruker Reflex III mass spectrometer equipped with a
nitrogen laser emitting at 337 nm, using ditranol as
matrix. UV–Vis Spectra in DMF solution were regis-
tered on an Ati-Unicam UV2 spectrophotometer and
the solid reflectance spectra on a Pye-Unicam SP-8-
100. Conductivity data were measured using freshly
prepared DMF solutions (ca. 10ꢀ3 M) at 25 °C with
a Metrohm Herisau model E-518 instrument. Electro-
chemical measurements were performed with a BAS
CV 27 voltammograph and a BAS A-4 XY register
using glassy carbon (B 5 mm) as the working elec-
trode, a platinum wire as the auxiliary electrode, and
In this paper we report the synthesis and character-
isation of cadmiun, zinc, lead, cobalt and nickel deriva-
tives of the ligand LH2OCH3 (Scheme 1). In these
complexes, depending on the preference for a coordi-
nated donor atom and the geometry for the metal ion,
the triazine acts as a bidentate ligand and as a bidentate
and bridging ligand.
a
double junction with a porous ceramic wick,
Ag/AgCl as the reference electrode, standardized for
the redox couple ferricinium/ferrocene (E1/2 = +0.400
V, DEp = 60 mV). Cyclic voltammetry studies of
LH2OCH3 and the complexes were carried out on
0.01 M solutions in dimethylformamide containing
0.1 M [NBu4][PF6] as the supporting electrolyte. The
range of potential studied was between +1.4 and
ꢀ2.2 V. All solutions were purged with nitrogen steam
for 5 min before measurement and the working elec-
trode was polished before each experiment with dia-
mond paste. The procedure was performed at room
temperature and a nitrogen atmosphere was main-
tained over the solution during the measurements.
Magnetic susceptibilities of powder samples were
Ph
Ph
OMe
N
NH
N
H
S
Scheme 1. Drawing of LH2OCH3.

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E. Lopez-Torres, M . A. Mendiola / Polyhedron 24 (2005) 1435–1444
´
1437
measured in the range 2–293 K with a SQUID magne-
tometer (MPMS, Quantum Design) in a 1-T external
magnetic field.
2.4. Methoxy-5,6-diphenyl-4,5-dihydro-2H-
[1,2,4]triazine-3-thione, LH2OCH3 [25]
Selected spectroscopic data: IR/cmꢀ1: 3184s and
2.2. Crystallography
3131s (NH); 1608w (C@N), 1550s (thioamide I), 846w
(thioamide IV). H NMR (300 MHz, CDCl3, 25 °C):
1
A crystal of compound 1a was mounted on a glass fi-
bre and transferred to a Bruker SMART 6K CCD area-
detector three-circle diffractometer with a MAC Science
Co., Ltd. Rotating Anode (Cu Ka radiation,
d = 3.1 (s, 3H, OCH3), 7.4–7.2 (m, 8H, Ph), 7.5 (m,
2H, Ph), 10.0 (d, 1H, NH), 12.1 (d, 1H, NH). 13C
NMR (300 MHz, CDCl3, 25 °C): 83.2 (CR4), 50.7
(CH3O), 126.5, 129.3, 133.7, 141.7 (Ph), 142.4 (CN),
169.7 (CS).
˚
k = 1.54178 A) generator equipped with Goebel mirrors
at settings of 50 kV and 110 mA. X-ray data were col-
lected at 296 K, with a combination of six runs at differ-
ent u and 2h angles, 3600 frames. The data were
collected using 0.3° wide x scans and a crystal-to-detec-
tor distance of 4.0 cm.
The substantial redundancy in data allows empirical
absorption corrections (SADABS) [20] to be applied using
multiple measurements of symmetry-equivalent reflec-
tions (ratio of minimum to maximum apparent trans-
mission: 0.566680). The unit cell parameters were
obtained by full-matrix least-squares refinements of
10487 reflections.
The raw intensity data frames were integrated with
the SAINT [21] program, which also applied corrections
for Lorentz and polarization effects.
The software package SHELXTL [22] 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 system-
atic absences and was confirmed using the structure
solution. The structure was solved by direct methods
(SHELXS-97) [23], completed with difference Fourier
2.5. [Cd(H2O)L2]2 (1)
A mixture of LH2OCH3 (0.50 g, 1.70 mmol) and
LiOH Æ H2O (0.07 g, 1.70 mmol) was dissolved in meth-
anol (25 mL). Then a solution of Cd(NO3)2 Æ 4H2O
(0.52 g, 1.70 mmol) in the same solvent (25 mL) was
added. The mixture was stirred for 6 h at room temper-
ature and the yellow solid formed was filtered off,
washed with methanol and dried ‘‘in vacuo’’. Yield:
40%; m.p. 200 °C. [(CdH2O)L2]2 (1329.4): Anal. Calc.
C, 54.68; H, 3.34; N, 12.76; S, 9.72. Found: C, 54.92;
H, 3.32; N, 13.05; S, 9.53%. KM (DMF, Xꢀ1
cm2 mLꢀ1): 5. m/z (FAB+): 643.0 ([CdL2 + 1]+, 7%),
752.9 ([Cd2L2 ꢀ 1]+, 3%), 1017.9 ([Cd2L3]+, 15%). Se-
lected spectroscopic data: IR (KBr, cmꢀ1): 1600w,
1573w (C@N), 1490s (NCS), 812w (thioamide IV).
1H NMR (300 MHz, DMSO-d6, 25 °C): 7.3–7.5 (m,
Ph). 13C NMR (300 MHz, DMSO-d6, 25 °C): 128.3,
128.5, 128.8, 129.0, 129.6, 130.4, 135.6, 135.8 (Ph),
150.8, 155.1 (CN), 180.7 (CS). 113Cd NMR (300
MHz, DMF/CDCl3, 25 °C): 202.0. Yellow crystals of
complex 1a, with the formula [Cd(DMF)L2]2 Æ 2DM-
F Æ 1/4H2O, suitable for X-ray analysis, were grown
by slow evaporation of a dimethylformamide solution
of complex 1.
syntheses, and refined with full-matrix least squares
using
2
SHELXL-97
[24] minimizing xðF 2o ꢀ F c2Þ .
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 con-
tained in the SHELXTL 6.10 program library. The H
atoms were introduced in calculated positions with
fixed C–H distances. The coordinated DMF molecules
were found to be greatly disordered, which was
modelled. The occupation factors for each position
are 43% for O1 and 57% for O2; 36% for C32A
and 64% for C32B; and 36% for C33A and 64% for
C33B.
2.6. [Zn(H2O)L2]2 (2)
Zn(NO3)2 Æ 6H2O (0.25 g, 0.85 mmol) dissolved in
methanol (10 mL) was added to a solution of
LH2OCH3 (0.25 g, 0.85 mmol) and LiOH Æ H2O (0.04
g, 0.95 mmol) in methanol (40 mL). The mixture was
stirred under reflux during 4 h. Then the yellow solid
formed was filtered off, washed with methanol and
vacuum dried. Yield: 51%; m.p. >260 °C.
[Zn(H2O)L2]2 (1228.8): Anal. Calc. C, 57.20; H, 3.81;
N, 13.35; S, 10.17. Found: C, 56.90; H, 3.44; N,
13.35; S, 10.14%. KM (DMF, Xꢀ1 cm2 mLꢀ1): 9. m/z
(MALDI-TOF): 923.7 ([Zn2L3]+). Selected spectro-
scopic data: IR (KBr, cmꢀ1): 1598w, 1578w (C@N),
1495s (NCS), 807w (thioamide IV). 13C CP/MAS
NMR: 126.0, 128.5, 130.3, 134.5 (Ph), 151.4, 155.1
(CN), 177.6 (CS).
2.3. Syntheses
All reagents and other solvents were obtained from
standard commercial sources and were used as received.
Pb(NO3)2 was synthesised from Pb(SCN)2 and nitric
acid, according to the procedure described in the
literature.

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E. Lopez-Torres, M . A. Mendiola / Polyhedron 24 (2005) 1435–1444
1438
2.7. [PbL2]2 (3)
([NiL2 + 1]+. Selected spectroscopic data: IR (KBr,
cmꢀ1): 1600w, 1579w (C@N), 1485s (NCS), 817w (thio-
amide IV).
To a solution containing LH2OCH3 (0.50 g, 1.68
mmol) and LiOH Æ H2O (0.07 g, 1.67 mmol) in methanol
(50 mL) was added a solution of Pb(NO3)2 (0.56 g, 1.69
mmol) in distilled water (5 mL). The mixture was stirred
under reflux for 6 h and the brown solid formed was fil-
tered off, washed with methanol, then distilled water and
vacuum dried. Yield: 68%; m.p. 222 °C with decomposi-
tion. [PbL2]2 (1470.4): Anal. Calc. C, 34.21; H, 2.49; N,
14.97, S, 11.40. Found: C, 34.48; H, 2.55; N, 14.84; S,
11.46%. KM (DMF, Xꢀ1 cm2 mLꢀ1): 7. m/z (FAB+):
472.0 ([PbL + 1]+, 100%), 737.1 ([PbL2 + 1]+, 4%),
1207.1 ([Pb2L3]+, 35%). Selected spectroscopic data: IR
(KBr, cmꢀ1): 1599w, 1581w (C@N), 1486s (NCS), 812
(thioamide IV). 1H NMR (300 MHz, DMSO-d6, 25
°C): 7.1–7.5 (m, Ph). 13C NMR (300 MHz, DMSO-d6,
25 °C): 128.4, 129.0, 129.6, 130.1, 136.6 (Ph), 151.9,
154.2 (CN), 178.7 (CS).
3. Results and discussion
The complexes were obtained in methanol in the pres-
ence of a basic medium, which induces the loss of the
methoxy group as a methanol molecule, probably due
to an acid–base reaction with the relatively highly acidic
N–H bond, yielding LH, according to a mechanism pre-
viously published [14].
Analytical data of complexes show 1:2 metal/ligand
stoichiometries for all the derivatives, except for com-
plex 4 where the ratio is 1:3, and the absence of nitrate
groups. These indicate that in all the complexes the li-
gand acts as a monoanion L and that in complex 4
the cobalt has been oxidised to Co(III). Oxidation of
Co(II) salts in the presence of thiosemicarbazone li-
gands in ethanol, methanol and chloroform is docu-
mented [26–28]. The possibility of oxidation increases
with the presence of a basic medium. Measurements
of magnetic susceptibility for complex 4 indicate that
2.8. [CoL3] (4)
A solution of Co(NO3)2 Æ 6H2O (0.46 g, 1.58 mmol) in
methanol (25 mL) was added to a solution of LH2OCH3
(0.47 g, 1.58 mmol) and LiOH Æ H2O (0.07 g, 1.67 mmol)
in methanol (25 mL). The mixture was stirred at room
temperature for 6 h. Then the green solid formed was fil-
tered off, washed with methanol and dried ‘‘in vacuo’’.
Yield: 33%; m.p. 200 °C. [CoL3] (850.9): Anal. Calc.
C, 63.46; H, 3.52; N, 14.80; S, 11.52. Found: C, 63.09;
H, 3.38; N, 14.58; S, 11.52%. KM (DMF,
Xꢀ1 cm2 mLꢀ1): 8. m/z (FAB+): 587.9 ([CoL2 + 1]+,
15%), 852.2 ([CoL3 + 1]+, 25%). Selected spectroscopic
data: IR (KBr, cmꢀ1): 1600w, 1579w (C@N), 1480s
(NCS), 815w (thioamide IV). 1H NMR (300 MHz,
DMSO-d6, 25 °C): 7.1–7.6 (m, Ph). 13C NMR (300
MHz, DMSO-d6, 25 °C): 128.73, 128.78, 128.81,
128.89, 128.95, 129.00, 129.11, 129.51, 129.56, 129.87,
130.01, 130.13, 130.25, 130.34, 130.37, 130.40, 131.31,
131.81, 131.85, 134.81, 134.83, 135.06, 135.13, 135.17,
135.42, 135.46 (Ph), 153.11, 153.25, 154.46, 154.63,
159.91, 160.13, 160.23, 160.36 (CN), 182.57, 183.27,
184.35, 184.70 (CS).
l
eff = 0 BM, so the complex is diamagnetic, which con-
firms the oxidation of the metal and the existence of a
low-spin octahedral complex. Conductivity measure-
ments in DMF indicate the presence of non-ionic spe-
cies in this solvent [29]. In the mass spectra of
complexes 1, 2 and 3 (Fig. 1) a peak corresponding to
the fragment [M2L3]+ can be observed, which indicates
the presence of a dinuclear species. Due to the analytical
data indicating the absence of nitrate groups, if the
complexes contain two metal ions they must contain
four ligands to get neutrality, and one of them is lost
to form a monopositive ion. The way to get a dinuclear
species could be due to the formation of sulfur bridges,
as occurs in many thiosemicarbazone complexes [30–
32]. Moreover the spectra show peaks corresponding
to different fragmentations of the complexes, owing to
the loss of L or M. The mass spectrum of complex 4
exhibits
a peak corresponding to the fragment
[CoL3 + 1]+ pointing out the presence of a complex con-
taining one cobalt and three deprotonated ligands.
Mass spectra of complex 5 shows a peak corresponding
to the fragment [NiL2 + 1]+, which indicates the pres-
ence of a species containing one metal ion and two
deprotonated ligands. Experimental isotopic distribu-
tions show the same patterns as the theoretical ones
for all compounds.
2.9. [NiL2] (5)
To a solution of LH2OCH3 (1.00 g, 3.40 mmol) and
LiOH Æ H2O (0.07 g, 1.67 mmol) in methanol (130 mL)
was added Ni(NO3)2 Æ 6H2O (0.50 g, 1.70 mmol) dis-
solved in the same solvent (15 mL). The mixture was
stirred at room temperature for 8 h and the brown solid
formed was filtered off, washed with methanol and dried
‘‘in vacuo’’. Yield: 39%; m.p. >260 °C. [NiL2] (586.7):
Anal. Calc. C, 61.36; H, 3.41; N, 14.32; S, 10.91. Found:
C, 61.03; H, 3.52; N, 14.16; S, 10.87%. KM (DMF,
Xꢀ1 cm2 mLꢀ1): 11. m/z (MALDI-TOF): 587.0
The electronic spectrum of complex 4 shows a band
centred at ca. 17.241 cmꢀ1 and reflectance spectrum
shows two bands at 16.667 and 20.000 cmꢀ1, which is con-
sistent with a octahedral low-spin Co(III) complex. The
spectrum of complex 5 shows a band at 20.000 cmꢀ1
which agrees with a square-planar environment [33].
,

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E. Lopez-Torres, M . A. Mendiola / Polyhedron 24 (2005) 1435–1444
´
1439
Fig. 1. FAB + spectrum of [PbL2]2 (3).
3.1. Crystal structure of [Cd(DMF)L2]2 Æ 2DMF Æ
1/4H2O
Cd–S bond distance with the monodentate sulfur atom
is shorter than those with the bridging sulfurs, which
˚
moreover are quite different (2.6342 and 2.8932 A).
Crystallographic data of complex 1a are summarised
in Table 1.
The crystal structure of the cadmium complex is
formed of discrete [Cd(DMF)L2] entities linked through
one sulfur atom of another thiosemicarbazone ligand,
which leads to the dinuclear centrosymmetric
[Cd(DMF)L2]2 species. The molecular structure is
shown in Fig. 2 and selected bond distances and angles
are summarised in Table 2. In the complex the Cd(II)
ion is in a distorted octahedral arrangement formed by
two amine nitrogen atoms, three sulfur atoms and the
oxygen of a DMF molecule. The two water molecules
present in complex 1 have been substituted by solvent
molecules, which present great disorder. The coordina-
tion mode of the ligand affords four four-member che-
late rings. The triazine rings are almost planar with a
Table 1
Crystal data and structure refinement for complex 1a
1a
Formula
C72H68.5N16CdO2S4O4.25Cd2
Molecular weight
Crystal system
Space group
1579.00
tetragonal
P4/n
Unit cell dimensions
˚
a (A)
˚
23.4137(4)
23.4137(4)
b (A)
˚
c (A)
13.8831(3)
90
a (°)
b (°)
c (°)
90
90
3
˚
V (A )
7610.7(2)
4
1.376
Z
˚
˚
maximum deviation of 0.0749 A for C(1) and 0.055 A
Dc (Mg mꢀ3
Absorption coefficient (mmꢀ1
F(000)
)
˚
for C(16). S(1) is 0.318 A under this plane and S(2)
˚
0.2487 A above. So the triazine that contains N(4),
)
5.963
32166
Goodness-of-fit on F2
Reflections collected
Independent reflections (Rint
1.070
48038
N(5) and N(6) is more planar than the one that contains
N(1), N(2) and N(3). The aromatic rings form with re-
spect to these planes dihedral angles of 35.75° for
C(3)–C(8), 44.77° for C(10)–C(15), 42.55° for C(18)–
C(23) and 38.63° for C(25)–C(30). Cd–N bond distances
)
7188 (0.0389)
98.3%
Completeness to theta = 70.53°
Absorption correction
Refinement method
SADABS v. 2.03
full-matrix least-squares on F2
R1 = 0.0437, wR2 = 0.1277
R1 = 0.0484, wR2 = 0.1322
˚
Final R1 and wR2 [I > 2r(I)]
R indices (all data)
are slightly different (2.322 and 2.306 A), the one belong-
ing to the ligand that acts as a bridge being shorter. The

a
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E. Lopez-Torres, M . A. Mendiola / Polyhedron 24 (2005) 1435–1444
1440
Fig. 2. Molecular structure of [Cd(DMF)L2]2 Æ 2DMF Æ 1/4H2O (1a). Thermal ellipsoids are shown at 50% probability. Hydrogen atoms are omitted
for clarity.
In the complex, owing to the deprotonation, there is a
considerable electronic delocalisation through the thio-
semicarbazone backbone. As a consequence all the
C–N bonds have almost the same length (Table 2),
monoanion L in all complexes. The band corresponding
to the CS moiety is shifted to lower frequencies, indicat-
ing coordination of the sulfur to the metal ion. The pres-
ence of two bands attributable to C@N bonds could
indicates the formation of a new imine group, due to
the loss of the methoxy group of the ligand LH2OCH3,
although the great electronic delocalisation in the ring
probably leads to there being only one C@N band and
the new band could be due to the hydrazinic CN. These
imine nitrogen atoms are not coordinated to the metal ion.
˚
which does not occur in LH2OCH3 (1.28–1.459 A). In
the complex the thione bonds are longer than in the pre-
˚
cursor ligand (1.628 A in LH2OCH3) and they are inter-
mediate between the theoretical C–S single and double
bonds, as is also the case of the N–N bonds [34]. In addi-
tion the N(3)–C(2)–C(3) and N(3)–C(8)–C(1) angles are
close to 120°, as would be expected for sp2 hybridisa-
tion, while in LH2OCH3 the corresponding angle is
108°, corresponding to sp3 hybridisation.
3.3. NMR Spectroscopy
The NMR assignments for LH2OCH3 are listed in
Section 2. The low solubility of complexes 2 and 5 made
3.2. IR Spectroscopy
1
it impossible to obtain H and 13C NMR spectra. In
The IR spectrum of LH2OCH3 is reported in
Section 2. The absence of a band in the 2600 cmꢀ1 re-
gion in any complex suggests the absence of a thiol
tautomer [35]. In the spectra of all complexes there are
no bands in the 3000–3300 cmꢀ1 region, which indicates
the absence of N–H bonds. Moreover bands attributable
to the nitrate group are not observed. The absence
of these bands confirms that the ligand acts as a
addition, the 13C CP/MAS NMR of complex 5 was re-
corded, but it did not show any clear signal, probably
due to a high heterogeneity in the sample. The 1H
NMR spectra of all the complexes only show a multiplet
in the aromatic region, corresponding to the phenyl
rings of the ligand. The absence of any signal corre-
sponding to amine protons supports the ligand deproto-
nation. The absence of the singlet attributable to the

a
E. Lopez-Torres, M . A. Mendiola / Polyhedron 24 (2005) 1435–1444
´
1441
Table 2
Table 2 (continued)
˚
Selected bond lengths (A) and angles (°) for complex 1a
C(17)–N(6)–C(16)
C(1)–S(1)–Cd(1)
117.1(3)
Cd(1)–N(4)
Cd(1)–O(2)
Cd(1)–O(1)
Cd(1)–N(1)
Cd(1)–S(1)
Cd(1)–S(2)#1
Cd(1)–S(2)
C(1)–N(3)
C(1)–N(1)
C(1)–S(1)
2.306(2)
2.310(9)
2.346(5)
2.522(3)
2.5300(9)
2.6342(9)
2.8932(9)
1.349(5)
1.353(4)
1.732(4)
1.332(5)
1.418(5)
1.338(4)
1.342(4)
1.347(4)
1.738(3)
1.325(4)
1.420(5)
1.332(4)
1.332(4)
1.334(4)
2.6342(9)
86.33(12)
93.76(10)
76.55(11)
96.25(3)
C(16)–S(2)–Cd(1)#1
C(16)–S(2)–Cd(1)
Cd(1)#1–S(2)–Cd(1)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx,
ꢀy + 1, ꢀz.
methoxy group at 3.3 ppm confirms the loss of the in-
serted methoxy group and the formation of a new
C@N bond.
C(2)–N(3)
C(2)–C(9)
C(9)–N(2)
C(16)–N(4)
C(16)–N(6)
C(16)–S(2)
C(17)–N(6)
C(17)–C(24)
C(24)–N(5)
N(1)–N(2)
N(4)–N(5)
S(2)–Cd(1)#1
In the 13C NMR spectra the signals corresponding
to the methoxy group and the tetrasubstituted carbon
atom have disappeared and a new signal corresponding
to an imine group is observed. The imine groups are
not bonded to the metal ion, as the X-ray diffraction
has established for complex 1a. In addition the signal
corresponding to the thione group is deshielded in all
complexes, suggesting the presence of metal–sulfur
bonds.
N(4)–Cd(1)–O(2)
N(4)–Cd(1)–O(1)
O(2)–Cd(1)–O(1)
N(4)–Cd(1)–N(1)
O(2)–Cd(1)–N(1)
O(1)–Cd(1)–N(1)
N(4)–Cd(1)–S(1)
O(2)–Cd(1)–S(1)
O(1)–Cd(1)–S(1)
N(1)–Cd(1)–S(1)
N(4)–Cd(1)–S(2)#1
O(2)–Cd(1)–S(2)#1
O(1)–Cd(1)–S(2)#1
N(1)–Cd(1)–S(2)#1
S(1)–Cd(1)–S(2)#1
N(4)–Cd(1)–S(2)
O(2)–Cd(1)–S(2)
N(2)–N(1)–Cd(1)
C(1)–N(1)–Cd(1)
N(1)–N(2)–C(9)
C(2)–N(3)–C(1)
N(5)–N(4)–C(16)
N(5)–N(4)–Cd(1)
C(16)–N(4)–Cd(1)
O(1)–Cd(1)–S(2)
N(1)–Cd(1)–S(2)
S(1)–Cd(1)–S(2)
S(2)#1–Cd(1)–S(2)
N(3)–C(1)–N(1)
N(3)–C(1)–S(1)
89.3(3)
83.92(14)
23.3(3)
The 13C NMR spectrum of complex 4 shows four
signals corresponding to CS groups, four to CN and
26 corresponding to aromatic carbon atoms. Two iso-
mers of octahedral complexes with asymmetric chelat-
ing ligands are possible. In the fac isomer, the A end
of each ligand is trans to the B end, and the three
ligands are equivalent. In the mer form, which has a
triple statistical probability, two of the A ends are trans
to each other, and all three ligands are chemically dis-
tinct [36]. Thus, if there is an isomer mixture four sets
of carbon resonances must be observed, as occurs. So
we can establish there is a mixture of fac and mer
isomers.
The 113Cd NMR spectrum of complex 1 in a DMF/
CDCl3 solution shows a peak at 202.04 ppm, which
indicates a coordination number of six for the cad-
mium ion. Sulfur ligands are most strongly deshielding,
while nitrogen and oxygen donor ligands have a wea-
ker deshielding effect on the Cd(II) ion [37]. Taking
this into account and by comparison with the complex
[CdLH6(NO3)2] (d = 177.8 ppm), with the ligand ben-
zilbisthiosemicarbazone LH6 in which the metal is in
a distorted octahedral arrangement with a N2S2O2
environment [38], the value of the 113Cd chemical shift
is in agreement with a N2S3O environment for cad-
mium ions.
95.23(9)
83.6(5)
106.7(3)
157.44(7)
91.2(3)
104.66(17)
62.43(7)
91.12(7)
108.6(5)
86.0(2)
166.38(7)
110.05(3)
59.20(7)
146.9(2)
145.1(2)
95.4(2)
119.5(3)
117.0(3)
119.7(3)
129.9(2)
108.2(2)
141.33(16)
89.17(7)
113.89(3)
83.75(3)
123.5(3)
120.8(3)
115.6(3)
119.3(3)
116.5(3)
120.0(3)
115.3(3)
123.2(3)
115.8(2)
121.0(3)
120.0(3)
119.8(3)
118.5(3)
119.1(3)
N(1)–C(1)–S(1)
N(3)–C(2)–C(9)
N(3)–C(2)–C(3)
N(2)–C(9)–C(2)
N(2)–C(9)–C(10)
N(4)–C(16)–N(6)
N(4)–C(16)–S(2)
N(6)–C(16)–S(2)
N(6)–C(17)–C(24)
N(5)–C(24)–C(17)
N(2)–N(1)–C(1)
C(24)–N(5)–N(4)
In sight of the data found, and taking into account
the results obtained with some organotin derivatives
[14], we can assume that the ligand L acts in all com-
plexes as at least as a NS chelate. The structure of com-
plex 2 could consist of a monomer, in which two sulfur
and two nitrogen atoms of two ligands occupy the base
of a square-base pyramid and with the oxygen of the
water molecule in the apex, or a dinuclear one as

a
E. Lopez-Torres, M . A. Mendiola / Polyhedron 24 (2005) 1435–1444
´
1442
3.4. Electrochemical behaviour
The cyclic voltammogram of LH2OCH3 in DMF
only shows an irreversible cathodic wave at ꢀ1.897 V,
which can be attributed to the reduction of the groups
present in the ligand.
The cyclic voltammogram of complex 1 between 1.4
and ꢀ2.2 V (Fig. 3) exhibits three cathodic waves at
ꢀ0.892, ꢀ1.482 and ꢀ1.847 V and an anodic one at
ꢀ0.261 V, related to the one at ꢀ0.892 V. This redox
couple, with E1/2 = ꢀ0.576 V, corresponds to Cd(II)/
Cd(I) process. The morphology of the first cathodic
peak is similar to that of the Cd(II)/Cd(I) process in
Cd(NO3)2 Æ 4H2O in DMF, although it is shifted to more
negative potentials.
On scanning from 1.0 to ꢀ2.2 V, the cyclic voltam-
mogram of complex 4 (Fig. 4) shows a redox couple at
E1/2 = ꢀ0.150 V, corresponding to a Co(III)/Co(II) pro-
cess, and two irreversible cathodic peaks corresponding
to ligand reduction processes. Analysis of the redox cou-
ples of complexes 1 and 4 in the interval 25–800 mV/s
shows a linear variation of ipc versus v1/2. A small depen-
dence of the potential peak with the scan rate is ob-
served, and the ipa–ipc ratio is close to unity. These
Fig. 3. Cyclic voltammogram of complex [Cd(H2O)L2]2 (1) in DMF;
v = 100 mV/s. Inset: the redox couple.
complex 1 shows. Complexes 1a and 2 show the same
spectroscopic characteristics and the same pattern in
the mass spectra. In particular, the mass fragment
[Zn2L3]+ would be difficult to explain without the pres-
ence of a dimeric species (molecular association during
the experiment would lead to the fragment
[Zn2L4 + 1]+). Hence the structure of complex 1 could
be expected for complex 2, with Zn(II) in a distorted
octahedral arrangement formed by two amine nitrogen
atoms, an oxygen of a water molecule and three sulfur
atoms, two of them acting as bridge, a structure that
has been found in other Zn(II) complexes with N2S li-
gands, with a dimeric structure via sulfur bridges [39].
In complex 3 a dimeric structure is also expected, where
two of the four ligands act also as bridges, so Pb(II) is in
a N2S3 environment in a pentacoordinate geometry.
However, the structure of complex 3 may be considered
as octahedral if the lone pair is considered as ‘‘occupy-
ing’’ one position, as is quite common for Pb(II) com-
plexes. Complex 4 presents the expected octahedral
geometry for Co(III), with a N3S3 environment for the
metal ion. In complex 5 the Ni(II) ion is in a square-pla-
nar arrangement with the two ligands bonded through
the sulfur atom and the amine nitrogen, so the Ni(II)
environment is N2S2. By comparison with other metal
derivatives previously published by us with this ligand
[14], we expect the formation of the cis isomer.
Fig. 4. Cyclic voltammogram of complex [CoL3] (4) in DMF; v = 100
mV/s. Inset: the redox couple.

a
E. Lopez-Torres, M . A. Mendiola / Polyhedron 24 (2005) 1435–1444
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In all the complexes the ligand acts as bidentate and
bonds to metal ions through the sulfur atom and the
deprotonated amine nitrogen, giving a four-member
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as well as by the ligand configuration. Complexes 1, 2
and 3 are dinuclear species, in which the sulfur atom
of two thiosemicarbazone ligands acts as a bridge be-
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Acknowledgements
´
We thank Cesar J. Pastor and Beatriz Souto Perez, of
the ‘‘Servicio Interdepartamental de Investigacion, Uni-
´
versidad Autonoma de Madrid’’ for the X-ray diffrac-
tion and Prof. Regino Saez and Dr. Julio Romero of
the ‘‘Universidad Complutense de Madrid’’ for the mag-
netic susceptibility measurements. We also thank DGI-
CYT for financial support (Project BQU2001-0151).
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Appendix A. Supplementary data
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Crystallographic Data Centre, 12 Union Road, Cam-
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033; e-mail: deposit@ccdc.cam.ac.uk, or on the web
www.ccdc.cam.ac.uk/conts/retrieving.html. Supplemen-
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