New neutral metal complexes from the 4-N-phenylthiosemicarbazone-2- pyridinecarboxaldehyde ligand -113Cd and207Pb NMR studies

Article abstract of DOI:10.1002/zaac.200700274

The metal complexes studied in this report derive from the ligand 4-N-phenylthiosemicarbazone-2-pyridinecarboxaldehyde, abbreviated HL, and the transition and post-transition metals manganese, iron, cobalt, nickel, copper, silver, zinc, cadmium and lead. The new complexes were obtained by an electrochemical procedure and were found to be of the form ML₂ ·nH₂O (n = 1-4) for divalent metals and ML · nH ₂O (n = 0, 4) for Cu and Ag metals. These complexes have been wholly characterized by elementalanalysis, mass spectrometry, infrared spectroscopy, magnetic measurements and molar conductivities. NMR studies in solution ( ¹H, ¹¹³Cd and ²⁰⁷Pb NMR) were also performed. [MnL₂] -CHCl₃ (1), [ZnL₂] · CH ₃CN (2) and [CdL₂] ·CH₃CN (3) could be crystallographically characterized and their crystal structures show the metal atoms in a distorted octahedral environment.

Full text of DOI:10.1002/zaac.200700274

DOI: 10.1002/zaac.200700274
New Neutral Metal Complexes from the 4-N-Phenylthiosemicarbazone-2-
pyridinecarboxaldehyde Ligand ؊ 113Cd and 207Pb NMR Studies
a,
b,
a
a
´
´
Manuel R. Bermejo *, Ana M. Gonzalez-Noya *, Miguel Martınez-Calvo , Rosa Pedrido , Marcelino
b
b
b
´
´
´
Maneiro , M. Isabel Fernandez , and Esther Gomez-Forneas
a
´
´
Santiago de Compostela/Spain, Universidade de Santiago de Compostela, Departamento de Quımica Inorganica
b
´
´
Lugo/Spain, Universidade de Santiago de Compostela, Departamento de Quımica Inorganica
Received May 3rd, 2007.
˜
Dedicated to Professor Alfonso Castineiras on the Occasion of his 65th Birthday
Abstract. The metal complexes studied in this report derive from
the ligand 4-N-phenylthiosemicarbazone-2-pyridinecarboxal-
dehyde, abbreviated HL, and the transition and post-transition me-
tals manganese, iron, cobalt, nickel, copper, silver, zinc, cadmium
and lead.
The new complexes were obtained by an electrochemical procedure
and were found to be of the form ML2 ·nH2O (n ϭ 1Ϫ4) for di-
valent metals and ML·nH2O (n ϭ 0, 4) for Cu and Ag metals.
These complexes have been wholly characterized by elemental
analysis, mass spectrometry, infrared spectroscopy, magnetic meas-
urements and molar conductivities. NMR studies in solution (1H,
113Cd and 207Pb NMR) were also performed. [MnL2]·CHCl3 (1),
[ZnL2]·CH3CN (2) and [CdL2]·CH3CN (3) could be crystallo-
graphically characterized and their crystal structures show the
metal atoms in a distorted octahedral environment.
Keywords: Transition metals; Thiosemicarbazone ligands; Electro-
chemical synthesis; NMR (113Cd and 207Pb); Crystal structures
Introduction
4-N-phenylthiosemicarbazone-2-pyridinecarboxaldehyde
(HLЈ, Scheme 1) [13]. Pharmacologic studies have proved
that the introduction of different groups in the 4-N position
of the thiosemicarbazone ligand has an important influence
in its biological activity [14, 15]. However, it has not been
completely proved the clear relationship between biological
activity and structure [16]. Accordingly, we have decided to
modify the previously reported ligand, H2LЈ, incorporating
a bulkier group in the 4-N position (H2L, Scheme 1). The
earlier work on this system is merely confined to some spec-
troscopies studies [17, 18]. The interaction of this ligand
with transition and post-transition metals by means of an
electrochemical procedure was carried out, and the results
achieved are reported herein.
Inorganic and bioinorganic chemists have shown a vast
interest in devising small molecules, which can act as
models for different metalloproteins or exhibit therapeutic
activity. For this purpose the thiosemicarbazone ligands
and their metal complexes have resulted very appropriate
[1Ϫ3]. Specifically, neutral copper complexes with this type
of ligands commenced recently to be used as radionuclide
agents [4, 5].
Thiosemicarbazone ligands reveal other important appli-
cations, for instance as anions receptors [6], as ionophores
[7] or for the HPLC separations and determinations of
metal ions since their capability to form highly stable com-
plexes [8].
During last years we have centred our efforts in the devel-
opment of a convenient synthetic route to neutral metal
complexes derived from a large variety of thiosemicarba-
zone ligands. As a result of these studies, we have been able
to stabilize neutral complexes with transition and post-tran-
sition metal ions using an electrochemical synthesis [9Ϫ12].
Lately, we have reported new metal derivatives of the ligand
* Prof. Dr. Manuel R. Bermejo
´
´
´
Departamento de Quımica Inorganica, Facultade de Quımica
Universidade de Santiago de Compostela
15782 Santiago de Compostela/ Spain
Fax number: ϩ 34 981597525
E-mail: qimb45@usc.es
Scheme 1
Z. Anorg. Allg. Chem. 2007, 633, 1911Ϫ1918
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1911

´
´
´
´
´
M. R. Bermejo, A. M. Gonzalez-Noya, M. Martınez-Calvo, R. Pedrido, M. Maneiro, M. I. Fernandez, E. Gomez-Forneas
Results and Discussion
from the electrochemical reaction of the zinc and cadmium
complexes allow isolation of yellow crystals of
[ZnL2]·CH3CN (2) and [CdL2]·CH3CN (3), respectively.
The electrochemical oxidation of a metal anode (Mn, Fe,
Co, Ni, Cu, Ag, Zn, Cd and Pb) in the presence of the
ligand HL in an organic solvent [19] has been used as an
efficient method to stabilize neutral metal complexes.
The reaction of HL with manganese, iron, cobalt, nickel,
zinc, cadmium and lead yields complexes: MnL2 ·H2O,
FeL2 ·2H2O, CoL2 ·4H2O, NiL2 ·H2O, ZnL2 ·2H2O,
CdL2 ·2H2O, and PbL2 ·3H2O. The electrochemical ef-
ficiency of the cell for these complexes was close to 0.5 mol
X-ray studies
Crystal structures of [MnL2]·CHCl3 (1), [ZnL2]·CH3CN (2)
and [CdL2]·CH3CN (3): These analyses show that 1, 2, and
3 have similar structures that consist of discrete molecules
ML2. These molecules contain two monodeprotonated li-
gand units and one metal centre. Additionally, zinc and
cadmium complexes contain one acetonitrile molecule as
solvate, whilst manganese complex is solvated by one mol-
ecule of chloroform.
ORTEP view of 1, 2 and 3 are shown in Figures 1, 2
and 3, respectively. Selected crystallographic data for the
complexes are summarised in Table 1. Bond lengths and
angles are listed in Table 2.
F
Ϫ1, which is in accordance with the following mechanism
for the reaction:
Cathode: 2HL ϩ 2eϪ Ǟ 2LϪ ϩ H2
Anode: 2LϪ ϩ M Ǟ ML2 ϩ 2eϪ
The syntheses of CuL·4H2O and AgL involve one electron
and the electrochemical efficiency of the cell was around
1 mol FϪ1. In these cases the proposed mechanism for the
reaction can be described as follows:
All of them crystallize in the monoclinic system, space
group P21/c for 1 and C2/c for 2 and 3. The structures of 2
1
Cathode: HL ϩ eϪ Ǟ LϪ ϩ /2 H2
Anode: LϪ ϩ M Ǟ ML ϩ eϪ
The metal compounds are obtained in high yield and purity.
They are solids apparently stable in the solid state and in
solution, with melting points over 300 °C.
These complexes have been characterized by elemental
analysis, mass spectrometry and magnetic measurements
(Table 6), infrared spectroscopy and molar conductivities
1
(Table 4) and H NMR studies (Table 5). For cadmium(II)
and lead(II) complexes we have also performed studies on
113Cd and 207Pb NMR.
Recrystallisation of the orange powder of MnL2 ·H2O
in chloroform lets us to isolate orange crystals of
[MnL2]·CHCl3 (1). Slow evaporation of the mother-liquors
Fig. 2 ORTEP plot of complex 2. Atoms showing the atomic
numbering scheme are represented by their 30 % probability ellip-
soids. Lattice CH3CN is not depicted. Hydrogen atoms are omitted
for clarity.
Fig. 1 ORTEP view of complex 1 showing the atomic numbering
scheme. Thermal ellipsoids are drawn at the 50 % probability level.
Lattice CHCl3 is not depicted. Hydrogen atoms are omitted for
clarity.
Fig. 3 ORTEP view of complex 3. Atoms showing the atomic
numbering scheme are represented by their 50 % probability level.
Lattice CH3CN is not depicted. Hydrogen atoms are omitted for
clarity.
1912
www.zaac.wiley-vch.de
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 1911Ϫ1918

New Neutral Metal Complexes
a)
Table 1 Crystal data and details of refinement of 1, 2 and 3
.
1
2
3
Formula
M. W.
C26H22MnN8S2
565.58
13.8267(2)
18.9985(3)
C26H22ZnN8S2
614.04
14.0266(13)
19.3208(12)
C26H22CdN8S2
623.04
13.9556(3)
19.8907(4)
10.7766(2)
˚
a/A
˚
b/A
˚
c/A
11.2970(2)
11.1553(10)
β/°
99.0070(10)
2930.98(8)
4
1.282
P21/c
monoclinic
0.16 ϫ 0.10 ϫ 0.06
1.49 to 28.32
105.523(8)
2912.9(4)
4
1.400
C2/c
monoclinic
0.20 ϫ 0.12 ϫ 0.12
3.99 to 74.92
108.0640(10)
2843.99(10)
4
1.455
C2/c
monoclinic
0.11 ϫ 0.07 ϫ 0.04
1.85 to 26.41
25402
3020 [R(int) ϭ 0.0509]
136
3
˚
V/A
Z
Dc/g cmϪ3
Space group
Crystal system
Crystal size/mm
θ range/°
Reflections collected
No. Unique reflections
No. Variables
µ /mmϪ1
51648
7298 [R(int) ϭ 0.0688]
280
3079
2960 [R(int) ϭ 0.0341]
187
2.790
0.621
0.944
F(000)
1164
1260
1256
Ϫ3
˚
Largest Peak and hole/e A
Final R indices [I>2sigma(I)]
R indices (all data)
1.528 and Ϫ1.593
R1 ϭ 0.0560, wR2 ϭ 0.1047
R1 ϭ 0.0842, wR2 ϭ 0.1143
0.356 and Ϫ0.342
R1 ϭ 0.0356, wR2 ϭ 0.0966
R1 ϭ 0.0750, wR2 ϭ 0.1110
3.355 and Ϫ1.810
R1 ϭ 0.0539, wR2 ϭ 0.1322
R1 ϭ 0.0642, wR2 ϭ 0.1375
a) Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as
supplementary publication nos. CCDCϪ645786 (1), 645787 (2), 645785 (3). Copies of the data can be obtained free on application to The
Director. CCDC. 12. Union Road. Cambridge CB2 1EZ. UK (Fax: int. code ϩ (1223)336-033; e-mail for inquiry: fileserv@ccdc.cam.ac.uk;
e-mail for deposition: deposit@ccdc.cam.ac.uk).
˚
Table 2 Selected bond lengths/A and angles/° for 1, 2 and 3.
Mn(1)-N(7)
Mn(1)-N(3)
Mn(1)-N(8)
Mn(1)-N(4)
Mn(1)-S(2)
Mn(1)-S(1)
2.2448(17)
2.2465(17)
2.2870(18)
2.2985(18)
2.5318(6)
2.5383(6)
Zn(1)-N(2)
Zn(1)-N(2)#1
Zn(1)-N(9)
Zn(1)-N(9)#1
Zn(1)-S(12)
Zn(1)-S(12)#1
2.252(2)
2.252(2)
2.158(2)
2.158(2)
2.4633(8)
2.4633(8)
Cd(1) N(3)
Cd(1)-N(3)#1
Cd(1)-N(4)
Cd(1)-N(4)#1
Cd(1)-S(1)
2.358(2)
2.358(2)
2.408(2)
2.408(2)
2.5720(12)
2.5720(12)
Cd(1)-S(1)#1
N(7)-Mn(1)-N(3)
N(7)-Mn(1)-N(8)
N(3)-Mn(1)-N(8)
N(7)-Mn(1)-N(4)
N(3)-Mn(1)-N(4)
N(8)-Mn(1)-N(4)
N(7)-Mn(1)-S(2)
N(3)-Mn(1)-S(2)
N(8)-Mn(1)-S(2)
N(4)-Mn(1)-S(2)
N(7)-Mn(1)-S(1)
N(3)-Mn(1)-S(1)
N(8)-Mn(1)-S(1)
N(4)-Mn(1)-S(1)
S(2)-Mn(1)-S(1)
171.74(7)
72.36(6)
103.48(6)
99.95(6)
72.34(6)
84.99(6)
74.81(5)
108.87(5)
147.12(5)
99.15(5)
112.71(5)
74.21(5)
92.55(5)
144.84(5)
101.58(2)
N(2)ϪZn(1)ϪN(2)#1
N(9)ϪZn(1)ϪS(12)#1
N(9)#1ϪZn(1)ϪS(12)#1
N(2)ϪZn(1)ϪS(12)
N(2)ϪZn(1)ϪS(12)#1
N(9)ϪZn(1)ϪN(9)
N(9)ϪZn(1)ϪN(2)#1
N(9)#1ϪZn(1)ϪN(2)#1
S(12)ϪZn(1)ϪS(12)
85.87(11)
113.71(6)
77.55(6)
151.34(6)
94.35(6)
163.53(11)
93.92(8)
73.85(8)
98.75(4)
N(3)-Cd(1)-N(3)#1
N(3)-Cd(1)-N(4)#1
N(3)#1-Cd(1)-N(4)#1
N(4)-Cd(1)-N(4)#1
N(3)#1-Cd(1)-S(1)
N(3)-Cd(1)-S(1)
N(4)-Cd(1)-S(1)
N(4)-Cd(1)-S(1)#1
S(1)-Cd(1)-S(1)#1
158.11(11)
93.77(8)
69.34(8)
82.22(11)
120.87(6)
73.76(6)
142.96(6)
97.19(6)
104.42(4)
and 3 contain a crystallographic twofold axis bisecting the
molecules. The environment around the metal atoms can be
described as distorted octahedral, where both ligand mol-
ecules act as tridentate and monoanionic. In any case the
disposition of these ligands drives to the formation of mer
type isomers.
It must be noted that complexes 2 and 3 are isotypical.
The disposition of the two ligands around the metal centre
determines the arrangement of these complex molecules in
the crystal cell. Therefore, the high symmetry exhibit by
complexes 2 and 3 leads to the formation of an ordered
network (see Figure 4), in which the solvent molecules
(acetonitrile) are accommodated inside.
Each ligand molecule exists in its deprotonated form LϪ,
coordinating to the metal centre through the donor set N2S,
formed by the pyridine nitrogen atom (N4 and N8 for 1,
N2 and N2#1 for 2 and N4 and N4#1 for 3), the imine
nitrogen atom (N3 and N7 for 1, N9 and N9#1 for 2 and
N3 and N3#1 for 3) and the thioamide sulfur atom (S1 and
S2 for manganese complex, S12 and S12#1 for zinc complex
and S1 and S1#1 for cadmium derivative). This octahedral
geometry is the most found in these metal complexes
Z. Anorg. Allg. Chem. 2007, 1911Ϫ1918
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1913

´
´
´
´
´
M. R. Bermejo, A. M. Gonzalez-Noya, M. Martınez-Calvo, R. Pedrido, M. Maneiro, M. I. Fernandez, E. Gomez-Forneas
Fig. 4 Illustration of the packing of molecules in complex 2 along
axis c.
[20Ϫ23], however other examples with coordination four or
five were also reported with related ligands [24, 25].
This coordination gives rise two five-membered chelate
Fig. 5 Partial scheme of the network formed by hydrogen bonds in 1.
rings with each ligand molecule. Two of the four angles sub-
tended at metal atom by adjacent equatorial atoms are big-
ger than the value of 90° for an ideal octahedral arrange-
values of the angles are also more divergent from the ideal
ment [99.97°, 112.68° for 1; 93.92°, 113.71° for 2, and
value of 90° and 180° for the equatorial and axial positions,
93.77°, 120.87° for 3], while the other two are smaller
respectively, in 1 than in [MnLЈ2]·H2O, indicating a higher
[72.31°, 74.27° for 1; 73.85°, 77.55° for 2, and 69.34°, 73.76°
deviation of the octahedral coordination in 1. This com-
pared study confirms the steric effect exerted by a bulkier
substituent on the 4-N position of the thiosemicarbazone
in the resulting structure of the metal complexes.
Significant intermolecular interactions via hydrogen
bonds (see Figure 5) can also be observed between the sul-
for 3]. The axial angle is also smaller than the ideal value
of 180° [147.18° for 1, 151.34° for 2 and 142.96° for 3].
The bond lengths MϪN(imine) are shorter than the
MϪN(pyridine) ones. And, as expected, the distances MϪS
are the most longer. These imine CϭN and thiolate CϪS
bond distances of the thiosemicarbazone threads are con-
sistent with strong coordination by the imine nitrogen and
the thiolate sulphur atoms [20Ϫ23].
In order to check the effect of different groups in the tail
of this kind of ligands, we have compared the bond dis-
tances and the angles of the manganese complex 1 reported
herein, with the previously prepared complex [MnLЈ2]·H2O
[13] (Table 3). The MnϪNimine and MnϪNpyridine in 1, phe-
nyl substituted in the 4-N position, are longer that those
found for [MnLЈ2]·H2O, methyl substituted in that posi-
tion. The MnϪS distances show the same tendency. The
phur atom of one molecule and the hydrazine nitrogen
˚
atom of a neighbouring molecule [N1···S2ϭ3.3758(18) A;
˚
˚
˚
S2···H1ϪN1
S2···H5ϪN1
ϭ
ϭ
147.77° and N5···S1ϭ3.3959(18) A;
146.35° for 1; N13···S12ϭ3.400(2) A;
S12···H13ϪN13 ϭ 146° for 2 and N1···S1ϭ3.460(3) A;
S1···H1AϪN1 ϭ 130.24°].
Magnetic characterization and conductivity
measurements
The magnetic moments at room temperature for the para-
magnetic compounds are close to those expected for mag-
netically diluted MII ions in an octahedral environment.
CuI, AgI, ZnII, CdII and PbII complexes are diamagnetic.
These values confirm the oxidation state ϩII (Mn, Fe, Co,
Ni, Zn, Cd, Pb) and ϩI (Cu, Ag) for the central atom and,
therefore, the monodeprotonation of the Schiff base ligand.
Molar conductivity measurements in 10Ϫ3 M DMF solu-
tions are in the range 4Ϫ23 ΩϪ1 cm2 molϪ1, which points
towards the non-electrolyte nature of these complexes [26],
as expected.
˚
Table 3 Compared study on selected bond lengths/A for manga-
nese complexes.
Reference
Mn-Nimine
Mn-Npy
Mn-S
[MnL2]·CHCl3 (1)
[MnLЈ2]·H2O
This work
2.2448(18)
2.2465(17)
2.2870(18)
2.2985(18)
2.5318(6)
2.5383(6)
Ref. [13]
2.0205(19)
2.0265(19)
2.114(2)
2.1183(19)
2.4225(8)
2.4378(7)
1914
www.zaac.wiley-vch.de
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 1911Ϫ1918

New Neutral Metal Complexes
Table 4 IR spectroscopy and conductivity measurements for the ligand and complexes.
b)
Compound
IR spectra /cmϪ1 a)
ν(CϭN)ϩ ν(C-N)
ΛM
ν(OH)
ν(NH)
ν(CϭS)
HL
Ϫ
3308 m, 3125 w
3287 w
3234 w
3242 w
3302 w
3300 w
3305 m
3297 w
3302 w
3278 w
1596 m, 1499 m
1599 w, 1494 w
1597 w, 1495 m
1599 m, 1492 s
1600 w, 1496 m
1599 m, 1494 s
1598 m, 1494 s
1594 w, 1495 w
1593 m, 1494 m
1599 w, 1487 s
1110 w, 755 m
1120 m, 749 w
1117 m, 752 w
1132 s, 758 w
1127 m, 750 w
1136 m, 766 w
1151 w, 746 m
1126 s, 749 w
1121 f, 750 w
1122 m, 749 w
Ϫ
4.4
5.2
15.7
4.6
4.6
4.1
6.3
5.1
22.5
MnL2 ·H2O
FeL2 ·2H2O
CoL2 ·4H2O
NiL2 ·H2O
CuL·4H2O
AgL
ZnL2 ·2H2O
CdL2 ·2H2O
PbL2 ·3H2O
3415 br
3402 br
3414 br
3414 br
3420 br
Ϫ
3411 br
3383 br
3437 br
a) s ϭ strong, m ϭ medium, w ϭ weak, sh ϭ shoulder, br ϭ broad; b) in Ω·Ϫ1 cm2 molϪ1
IR spectroscopy and mass spectrometry
NMR spectroscopy
1
The most significant infrared bands for these complexes are
collected in Table 4. The partial deprotonation of the ligand
is observed by the disappearance of one of the bands as-
signed to ν(N-H) in the free ligand [27]. Bands correspond-
ing to ν(CϭN) and ν(C-N) modes appear slightly shifted
and overlapped to ν(CϭC) absorptions in all complexes,
indicating metal coordination to the pyridine and imine ni-
trogen atoms. The coordination to the thioamide sulphur
atom is corroborated by the displacements of the bands
ν(CϭS). Besides, other bands due to the SH group between
2600 and 2500 cmϪ1 are not present, in agreement with the
thione form of the ligand and with the presence of bands
around 750 cmϪ1 for ν(CϭS) [13, 28].
The H NMR spectra of the ligand HL and its zinc, cad-
mium and lead complexes were recorded in dmso-d6 at
room temperature, and the relevant data are collected in
Table 5. The attempts of recording the spectrum for the
silver complex were unsuccessful, due to the low solubility
of this compound. In the case of the copper complex the
spectrum could be recorded, indicating the presence of cop-
per(I) species in solution; however its interpretation was not
possible due to the poor quality of this spectrum.
1
The superposition of the H NMR spectrum of the free
ligand with those of the complexes is illustrated in Figure 6.
The compared study of these spectra allows us to draw the
following conclusions:
Finally, all spectra, except the silver one, show a broad
band about 3400 cmϪ1, according with the presence of co-
ordinated and/or lattice water.
(a) In all cases, it is observed the disappearance of the NH
hydrazine protons (H1) present in the free ligand, in
agreement with the monodeprotonation of the ligand
[29].
The electrospray mass spectra exhibit peaks assigned to
[ML2]ϩ fragments for most complexes, indicating the coor-
dination of two ligand units to the metal centres. Since in
the spectra of iron, cobalt, nickel and lead the pattern of
fragmentation is similar to that described for manganese 1,
zinc 2 and cadmium 3 complexes, crystallographically
solved, the same structure for these complexes could be de-
duced. In the case of copper and silver compounds, only
peaks due to [ML]ϩ fragments are present.
(b) The signal due to the NH-Ph group (H2) remains in
the spectra of these complexes, and it’s shifted to higher
field. This effect is more pronounced for the lead
complex.
(c) The imine hydrogen atom (H5) shows a shift to lower
field for all the complexes, indicating a withdrawal of
charge from the imine group upon coordination. This
1
Table 5 Some relevant H NMR data (in ppm) for the ligand and the diamagnetic compounds.
Compound
HL
H1
H2
H3
H4
H5
H6
H7
H8
H9
H10
12.01
(s, 1H)
10.24
(s, 1H)
8.57
(d, 1H)
8.41
(d, 1H)
8.19
(s, 1H)
7.85
7.54
(d, 2H)
7.37
(m, 1H)
7.37
(m, 2H)
7.21
(t, 1H)
(atb), 1H)
a)
ZnL2 ·2H2O
CdL2 ·2H2O
PbL2 ·3H2O
no
9.46
(s, 1H)
7.95
(d, 1H)
7.66
(d, 1H)
8.74
(s, 1H)
7.90
(at, 1H)
7.83
(d, 2H)
7.35
(at, 1H)
7.25
(at, 2H)
6.95
(t, 1H)
no
no
9.48
(s, 1H)
8.06
(d, 1H)
7.66
(d, 1H)
8.67
(s, 1H)
7.93
(at, 1H)
7.84
(d, 2H)
7.41
(at, 1H)
7.26
(at, 2H)
6.96
(t, 1H)
9.00
8.76
7.75
8.71
7.97
7.71
7.44
7.19
6.87
(s, 1H)
(d, 1H)
(d, 1H)
(s, 1H)
(at, 1H)
(d, 2H)
(at, 1H)
(at, 2H)
(t, 1H)
a) non observable; b) apparent triplet
Z. Anorg. Allg. Chem. 2007, 1911Ϫ1918
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1915

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M. R. Bermejo, A. M. Gonzalez-Noya, M. Martınez-Calvo, R. Pedrido, M. Maneiro, M. I. Fernandez, E. Gomez-Forneas
Fig. 6 1H NMR spectra in dmso-d6 at room temperature for HL,
ZnL2 ·2H2O, CdL2 ·2H2O and PbL2 ·3H2O.
signal is flanked by satellites arising from spin-spin
coupling to 111/113Cd in the cadmium complex spectrum
indicating that this complex is kinetically inert on the
NMR timescale.
(d) The pyridine aromatic protons (H3, H4, H6 and H8) are
Fig. 7 Multinuclear NMR spectra: a) 113Cd NMR for 3; 113Cd
also affected on coordination, mainly the protons in or-
NMR for CdLЈ2 ·H2O [13]; 207Pb NMR for PbL2 ·3H2O.
tho position respect to the nitrogen atom (H3 and H4).
This could be attributed to the coordination of the met-
als to the pyridine nitrogen atom [9].
We were keen to further investigate the solution behav-
iour of the cadmium and lead complexes. For this purpose
we have recorded their 113Cd and 207Pb NMR spectra.
The 113Cd spectrum of complex 3, in a dmso-d6 solution,
shows a unique signal at 405.8 ppm (Figure 7a). This value
is rather similar to that observed for other six-coordination
complexes with a kernel [N4S2] [30]. Therefore, it seems that
this cadmium complex retains in solution the structure
showed in solid state. The change of the phenyl group by
the methyl one in the 4-N position of these ligands affects
somewhat the displacement of the signal, from 405.8 to
410.2 ppm (Figure 7b). It is well known that the shielding
of 113Cd NMR signal increases when the donor atoms
change and/or the coordination number is increased [31].
This effect can be exemplified by the comparison between
the 113Cd chemical shift values showed by a complex with
a [N3S2] kernel (305 ppm), described by us in literature [32],
and the herein presented (405.8 ppm) containing a [N4S2]
core.
(e) The aromatic signals of the phenyl group (H7, H9 and
H10) experiment a slight change to higher field, with the
exception of H7 which shifts to lower field.
It must be noted that zinc and cadmium complexes exhi-
bit very similar NMR spectra. Nevertheless, the spectrum
of the lead complex is apparently quite different, showing
changed displacements of the signals. This fact could be
related with the structure presented for these species in solid
state. Zinc and cadmium complexes reveal a distorted octa-
hedral coordination around the metal centre, whilst the
coordination polyhedron for the lead compound may be
altered by the presence of the metal lone pair, as it was
previously found for the related PbLЈ2 [13].
On the other hand, the lead spectrum does not show sig-
nals attributed to the free ligand. It seems to indicate that
this complex is stable in solution, contrary to the behaviour
observed for the lead complex with a similar ligand 4-N-
methylthiosemicarbazone-2-pyridinecarboxaldehide
[13].
Relatively few 207Pb NMR spectroscopy studies have
been reported on soluble Pb(II) coordination compounds.
In spite of this, it is known some information that correlates
chemical shifts with coordination numbers and nature of
the donor set for this kind of complexes. The lead(II) com-
plex prepared by us shows a single signal at Ϫ309.7 ppm
Besides, the quality of these 1H NMR spectra is better than
that showed by the related complexes with the latter ligand.
This fact points to the 4-N substitution is involved with the
capability of the thiosemicarbazones to stabilize metal ions
in solution.
1916
www.zaac.wiley-vch.de
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 1911Ϫ1918

New Neutral Metal Complexes
trometer, whilst Electrospray was performed on a Hewlett-Packard
LCϪMSD 1100 instrument (positive ion mode, 98:2
MeOHϪHCOOH as mobile phase, 75 to 200 V). Room tempera-
ture magnetic susceptibility was measured using a Digital Measure-
ment system MSB-MKI, calibrated using mercury tetrakis(isothi-
ocyanato)cobaltate(II). Conductivity measurements were obtained
at 25 °C from 10Ϫ3 M solutions in DMF on a CRISON Basic 30
instrument.
(Figure 7c), in dmso-d6 solution, which is similar to the
value observed for a previous reported complex with the
metal centre in a [N3S2] environment (Ϫ304 ppm) [32], and
close to that corresponding to a coordination number six.
Having these data in mind, a coordination number six could
be tentatively proposed for this complex in solution. Unfor-
tunately, all attempts to obtain single crystals suitable for
X-ray diffraction for this lead complex were vain, and for
that reason it has not been possible to correlate the poten-
tial structure showed in solution with that presented in
solid state.
Syntheses
Preparation of 4-N-phenylthiosemicarbazone-2-pyridinecarboxal-
dehyde, HL. To a solution of 2-pyridinecarboxaldehyde (0.37 mL,
3.9 mmol) in ethanol (250 cm3) was added 4-N-phenylthiosemicar-
bazide (0.652 g, 3.9 mmol). The solution was heated under reflux
over a 6 h period, concentrated with a Dean Stark trap to ca.
30 cm3. The white precipitate formed was collected by filtration.
The resulting solid was finally washed with diethylether (3 ϫ
10 cm3) and dried in vacuo. M.p. 198 °C. This ligand was charac-
terized by elemental analysis and mass spectrometry (Table 6), in-
frared (Table 5) and 1H NMR spectroscopies (Table 6). In order to
assign correctly the aromatic protons a COSY experiment was also
performed. The 13C NMR spectrum shows 9 signals between 120.7
and 153.4 ppm, assigned to the aromatic protons. Other two signals
due to CϭN and CϭS groups are also present.
Conclusions
The electrochemical method has been shown to be a simple
and effective approach to prepare neutral transition and
post-transition metal complexes with this type of thiosem-
icarbazones with high purity and good yield. We have dem-
onstrated that the presence of the phenyl group in the 4-N
position of the ligand, a bulkier substituent than the methyl
one, favours the capability of this thiosemicarbone to stabil-
ize metal ions. This effect is also stated in the structure of
these metal complexes in solid state, as well, in their behav-
iour in the NMR studies in solution.
Synthesis of the Metal Complexes. The compounds were obtained
using an electrochemical procedure [33] improved by us [34]. An
acetonitrile solution of the ligand was electrolyzed using a platinum
wire as the cathode and a metal plate or platelet (in the case of
manganese) as the anode. The cell can be summarised as: Pt(Ϫ)ΗHL
ϩ MeCNΗM(ϩ), where M ϭ Mn, Fe, Co, Ni, Cu, Ag, Zn, Cd and
Pb. The synthesis is typified by the preparation of CdL2 ·2H2O. A
solution (0.1 g, 0.39 mmol) of the ligand in acetonitrile (80 cm3),
containing 10 mg of tetraethylammonium perchlorate as support-
ing electrolyte, was electrolyzed for 1.2 h. using a current of 10 mA.
The resulting pale yellow solid was filtered off, washed with diethyl
ether and dried in vacuo. (CAUTIONS: although no problem has
been encountered in this work, all perchlorate compounds are po-
tentially explosive, and should be handled in small quantities and
with great care. In addition, lead is a highly toxic cumulative poi-
son, and lead complexes should be handled carefully). Slow evapor-
ation from the mother liquors produces yellow crystals of
[CdL2]·CH3CN (3), useful for X-ray studies.
Experimental Part
General: All solvents, 2-pyridinecarboxaldehyde and 4-N-phenyl-
thiosemicarbazide are commercially available and were used with-
out further purification. Iron, cobalt, nickel, copper, silver, zinc,
cadmium and lead were purchased from Aldrich and used as sheets
0.5 mm thick. Manganese (Stream Chemical) was used as platelets.
Metals were cleaned of oxide in dilute hydrochloric acid prior to
electrolysis. Elemental analyses of C, H, N and S were performed
on a Carlo Erba EA 1108 analyser. 1H and multinuclear NMR
(
113Cd and 207Pb) spectra were recorded on a Varian INOVA 400
and a Bruker AMX-500 spectrometers respectively, using dmso-d6
as solvent. Chemical shifts are expressed relative to tetramethylsil-
ane (1H NMR), 0.1 M Cd(ClO4)2 113Cd NMR) and neat tetra-
(
methyllead using
a saturated solution of PbPh4 in CDCl3
(Ϫ178 ppm) as external reference (207Pb NMR). IR spectra were
recorded as KBr pellets on a Mattson Cygnus 100 spectrophoto-
meter in the range 4000Ϫ500 cmϪ1. Mass spectrometry (Electronic
Impact) was performed on a Hewlett Packard 5988A mass spec-
The other complexes were obtained by the same method, using the
appropriate metal anode. In the case of the copper derivative, a
Table 6 Elemental analysis and some selected data for the complexes
Compound
Yield
Colour
Found (Calcd.) (%)
MS (amu)a)
µ (BM)
% N
% C
% H
% S
HL
90
77
68
75
75
96
70
74
78
68
White
Orange-red
Green
Brown
Brown
Brown
Yellow
Yellow
Yellow
Yellow
21.5 (21.9)
19.2 (19.2)
18.5 (18.6)
17.0 (17.5)
19.4 (19.1)
15.5 (15.8)
15.5 (15.4)
18.4 (18.3)
16.9 (17.0)
12.8 (14.5)
60.3 (60.9)
52.1 (53.5)
52.0 (51.8)
48.1 (48.7)
53.2 (53.2)
43.4 (44.0)
42.6 (43.0)
50.8 (51.0)
46.7 (47.4)
39.8 (40.5)
4.5 (4.7)
3.7 (4.1)
3.7 (4.3)
3.8 (4.7)
3.9 (4.1)
3.1 (4.2)
3.0 (3.0)
3.6 (4.3)
3.3 (4.0)
3.7 (3.7)
11.8 (12.5)
10.1 (11.0)
10.6 (10.6)
10.6 (10.0)
9.9 (10.9)
8.1 (9.0)
8.4 (8.8)
10.5 (10.5)
9.4 (9.7)
256 (60)b)
565 (66)
566 (100)
569 (100)
568 (66)
318 (100)
406 (25)
569 (60)
623 (98)
719 (66)
Ϫ
MnL2 ·H2O
FeL2 ·2H2O
CoL2 ·4H2O
NiL2 ·H2O
CuL·4H2O
AgL
ZnL2 ·2H2O
CdL2 ·2H2O
PbL2 ·3H2O
6.1
5.5
5.2
3.5
dc)
d
d
d
d
6.4 (8.3)
a) Electrospray for complexes and Electronic Impact for ligand; b) relative abundance in %; c) diamagnetic
Z. Anorg. Allg. Chem. 2007, 1911Ϫ1918
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1917

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M. R. Bermejo, A. M. Gonzalez-Noya, M. Martınez-Calvo, R. Pedrido, M. Maneiro, M. I. Fernandez, E. Gomez-Forneas
´ ´
[13] M. R. Bermejo, A. M. Gonzalez-Noya, M. Martınez-Calvo,
vigorous nitrogen stream was flowing through the reaction mixture,
in order to avoid the oxidation of the copper(I) ion to the cop-
per(II). Recrystallisation of the powder of MnL2 ·H2O in chloro-
form lets us to isolate red crystals of [MnL2]·CHCl3 (1). Slow evap-
oration from the mother liquors of the reaction of ZnL2 ·2H2O
yields yellow crystals of [ZnL2]·CH3CN (2).
´
R. Pedrido, M. J. Romero, M. I. Fernandez, M. Maneiro, Z.
Anorg. Allg. Chem. 2007, 633, 807.
[14] P. W. Sadler, Ann. NY Acad. Sci. 1965, 130, 71.
[15] M. Belicchi Ferrari, F. Bisceglie, G. Pelosi, T. Tarasconi, R.
Albertini, S. Pinelli, J. Inorg. Biochem. 2001, 87, 137.
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c) I. H. Hall, M. C. Miller, D. X. West, Metal-Based Drugs.
1997, 4, 89.
X-Ray Crystallographic Studies. Crystals of 1, 2 and 3 suitable for
X-ray diffraction studies were obtained as described above. Data
for complex 1 and 3 were collected on an Bruker X8 Kappa
APEXII, using a graphite-monochromated Mo-Kα radiation (λ ϭ
˚
0.71073 A), at T ϭ 100.0(1) K. Data for complex 2 were collected
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on an Enraf Nonius TurboCAD4 using a graphite-monochromated
˚
Cu-Kα radiation (λ ϭ 1.54180 A), at T ϭ 293(2) K. Detailed data
collection and refinement of the compounds are summarized in
Table 1. The structures were solved by direct methods, and then
were refined by full-matrix, least-squares bases on F2 [35Ϫ37]. The
figures were drawn using the program ORTEP3 [38].
´
´
[19] M. R. Bermejo, A. M. Gonzalez-Noya, M. Fondo, A. Garcıa-
´
Deibe, M. Maneiro, J. Sanmartın, O. L. Hoyos, M. Watkinson,
New J. Chem. 2000, 24, 235.
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Acknowledgements. This work was supported by Xunta de Galicia
(PGIDIT04PXIC20902PN and PGIDIT06PXIB209043PR) and
´
´
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[21] M. C. Rodrıguez-Argue¨lles, E. C. Lopez-Silva, J. Sanmartın,
A. Bacchi, C. Pelizzi, F. Zani, Inorg. Chim. Acta 2004, 357,
2543.
´
Ministerio de Ciencia y Tecnologıa of Spain (BQU2003-00167). M.
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Martınez-Calvo and R. Pedrido thank Xunta de Galicia for the
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Marıa Barbeito and Isidro Parga Pondal contracts, respectively.
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www.zaac.wiley-vch.de
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 1911Ϫ1918