Transition metal complexes with thiosemicarbazide-based ligands. Part LVI: Nickel(II) complex with 1,3-diphenylpyrazole-4-carboxaldehyde thiosemicarbazone and unusually deformed coordination geometry

Article abstract of DOI:10.1016/j.poly.2007.04.012

Synthesis of a new nickel(II) complex, [Ni(Ph₂PzTSC-H)₂] with 1,3-diphenylpyrazole-4-carboxaldehyde thiosemicarbazone (Ph₂PzTSC), is described. The compounds have been characterized by elemental and thermal analysis, molar conductivity and spectral (UV-Vis, IR, ¹H NMR, and ¹³C NMR) measurements. In the case of complex the magnetic measurement has been also performed. Crystal and molecular structures of both the free ligand and the complex have been determined by single crystal X-ray analysis. It was found that the ligand coordinates in a bidentate NS fashion, in its deprotonated thioenolato form. The cis-square-planar geometry of the complex is significantly distorted tetrahedrally. The Cambridge Structural Database (CSD) study has been performed to obtain geometrical and structural informations on similar nickel(II) complexes in order to compare structural data.

Full text of DOI:10.1016/j.poly.2007.04.012

Polyhedron 26 (2007) 3783–3792
www.elsevier.com/locate/poly
Transition metal complexes with thiosemicarbazide-based ligands.
Part LVI: Nickel(II) complex with
1,3-diphenylpyrazole-4-carboxaldehyde thiosemicarbazone
and unusually deformed coordination geometry
a
b
b
-
´
´
Vukadin M. Leovac , Sladana B. Novakovic , Goran A. Bogdanovic ,
c,
a
a
*
ˇ
´
´ ´
´ ´
ˇ
´
Milan D. Joksovic , Katalin Meszaros Szecsenyi , Valerija I. Cesljevic
a
Faculty of Sciences, University of Novi Sad, Trg D.Obradovic´a 3, 21000 Novi Sad, Serbia
b
ˇ
VINCA Institute of Nuclear Sciences, P.O. Box 522, Belgrade 11001, Serbia
Faculty of Sciences, University of Kragujevac, R. Domanovica 12, 34000 Kragujevac, Serbia
c
Received 6 February 2007; accepted 6 April 2007
Available online 27 April 2007
Abstract
Synthesis of a new nickel(II) complex, [Ni(Ph2PzTSC-H)2] with 1,3-diphenylpyrazole-4-carboxaldehyde thiosemicarbazone
(Ph2PzTSC), is described. The compounds have been characterized by elemental and thermal analysis, molar conductivity and spectral
(UV–Vis, IR, 1H NMR, and 13C NMR) measurements. In the case of complex the magnetic measurement has been also performed. Crys-
tal and molecular structures of both the free ligand and the complex have been determined by single crystal X-ray analysis. It was found
that the ligand coordinates in a bidentate NS fashion, in its deprotonated thioenolato form. The cis-square-planar geometry of the com-
plex is significantly distorted tetrahedrally. The Cambridge Structural Database (CSD) study has been performed to obtain geometrical
and structural informations on similar nickel(II) complexes in order to compare structural data.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Nickel(II) complex; Thiosemicarbazone; Spectroscopic and TA studies; Crystal structure; CSD study
1. Introduction
On the other side, many pyrazole derivatives are known
to exhibit also a wide range of biological properties. Partic-
ularly, arylpyrazoles are important in medicinal and pesti-
cidal chemistry [6]. Recently, some arylpyrazoles were
reported to have non-nucleoside HIV-1 reverse transcrip-
tase inhibitory activity [7]. Extensive studies have been
devoted to arylpyrazole derivatives such as Celecoxib, a
well-known cyclooxygenase-2 inhibitor [8–11]. More
recently, pyrazole derivatives as high affinity and selective
A2B adenosine receptor antagonists have been reported
[12].
A number of N-heterocyclic thiosemicarbazones and
their metal ion complexes have attracted considerable
interest in chemistry and biology, owing to their potentially
beneficial biological activities (antibacterial, antimalarial,
antiviral, etc.), which have often been related to a chelation
phenomenon with trace of metal ions [1–5]. Heterocyclic
thiosemicarbazones are believed to exercise their beneficial
therapeutic properties in mammalian cells by inhibiting
ribonucleotide reductase in the synthesis of DNA precur-
sors [4].
The well-documented biological activities of N-hetero-
cyclic thiosemicarbazones have prompted further investi-
gation on the coordination chemistry of such ligands
during the last period [5,13] with the recommendation that
*
Corresponding author. Tel.: +381 34336223; fax: +381 34335040.
´
E-mail address: mjoksovic@kg.ac.yu (M.D. Joksovic).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.04.012

3784
V.M. Leovac et al. / Polyhedron 26 (2007) 3783–3792
1H NMR (200 MHz, DMSO-d6): 7.38–7.70, m (8H, Ar);
7.80, br s (1H, NH2); 7.90, d (2H, Ar, J = 7.86 Hz, ortho-
H, N-substituted phenyl); 8.22, s (1H, Pz); 8.27, br s (1H,
NH2); 9.19, s (1H, CH@N); 11.34, br s (1H, NH).
13C NMR (200 MHz, DMSO-d6): 117.43; 118.66;
127.15; 127.85; 128.30; 128.75; 128.91; 129.85; 132.28;
135.10; 139.20; 151.52; 177.72.
S
C
CH
N
NH
NH2
4
3
2
5
N
N1
IR (KBr pellets): 3326, 3257, 3140, 1618, 1598, 1543,
1500, 1221, 1098, 1064, 831, 807, 755, 704, 687 cmÀ1
.
2.3. Preparation of [Ni(Ph2PzTSC-H)2]
Fig. 1. Chemical structure of Ph2PzTSC.
Ni(CH3COO)2 Æ 4H2O (0.25 g, 1 mmol) was dissolved in
methanol (10 cm3) under heating and the solution was
mixed with a warm solution of Ph2PzTSC (0.32 g, 1 mmol)
in acetone (20 cm3). The heating was continuated for sev-
eral minutes. After 10 h of standing, the brown crystals
were filtered and washed with acetone and dried over anhy-
drous calcium chloride Yield: 0.16 g, 46%.
structural variation on the heterocyclic ring might bring
out significant enhancement in their biological effects,
especially in corresponding metal complexes, often with
novel structural information. Synthesis and spectroscopic
characterization of nickel(II) complexes with some pyraz-
olyl thiosemicarbazones, such as 5-methyl-3-formylpyraz-
ole-3-substituted thiosemicarbazones have been reported
by other authors [14–16]. As a part of our investigation
toward synthesis and structural characterization of new
compounds containing biorelevant pyrazolyl thiosemicar-
bazones, the present paper reports the synthesis, spectro-
scopic, and structural properties of 1,3-diphenylpyrazole-
4-carboxaldehyde thiosemicarbazone ligand (Ph2PzTSC,
Fig. 1) and its nickel(II) complex.
Anal. Calc. for C34H28N10NiS2: C, 58.38; H, 4.03; N,
20.02; Ni, 8.39. Found: C, 58.42; H, 3.98; N, 20.12; Ni,
8.42%. kM(DMF) = 3.3 S cm2 molÀ1
. /
UV–Vis: (cmÀ1
loge): ꢀ33300 (4.0); 30210 (4.3); 25500 sh (3.7); 19300
sh (2.1). sh (shoulder).
1H NMR (200 MHz, DMSO-d6): 6.97–7.19, m (7H; 5H,
phenyl and 2H, NH2); 7.49, s (1H, Pz); 7.50, d (1H, Ar,
J = 7.36Hz, para-H, N-substituted phenyl); 7.65, t, (2H,
Ar, J = 7.66Hz, meta-H, N-substituted phenyl); 8.03, d,
(2H, J = 7.77Hz, ortho-H, N-substituted phenyl); 9.84, s
(1H, CH@N, azomethine).
2. Experimental
13C NMR (200 MHz, DMSO-d6): 114.29; 119.89;
127.62; 127.86; 128.44; 128.83; 129.88; 130.10; 130.89;
139.23; 150.17; 152.68; 173.46.
2.1. Reagents and starting materials
IR (KBr pellets): 3466, 3284, 3067, 1626, 1596, 1526,
Solvents and reagents were obtained from commercial
sources. The solvents were purified using the established
method [17]. Thiosemicarbazide and nickel(II) acetate tet-
rahydrate were purchased from Aldrich Chemicals, USA.
1,3-Diphenylpyrazole-4-carboxaldehyde was synthesized
according to Rathelot et al. procedure [18].
1513, 1504, 1219, 956, 705, 672 cmÀ1
.
2.4. Physical measurements
Elemental (C, H, N) analysis of the samples was carried
out by standard micromethods in the Center for Instru-
mental Analysis, Faculty of Chemistry, Belgrade. Nickel
content was determined by the complexometric titration
with EDTA method, upon the destruction of complex with
the mixture of concentrated H2SO4 and HNO3. Molar con-
ductivity of freshly prepared 1 · 10À3 mol dmÀ3 solution
was measured on a Jenway 4010 conductivity meter. IR
spectra were recorded on a Perkin Elmer Spectrum One
2.2. Preparation of Ph2PzTSC
The Ph2PzTSC ligand was prepared by refluxing the
mixture of the 1,3-diphenylpyrazole-4-carboxaldehyde
(1.24 g, 5 mmol) and thiosemicarbazide (0.45 g, 5 mmol)
in ethanol (20 cm3) for 4 h. One drop of glacial acetic acid
was previously added into the mixture. After cooling, the
white precipitate was filtered, washed with cold chloroform
in order to remove the traces of unchanged aldehyde, and
dried over anhydrous calcium chloride. Yield: 1.25 g,
78%. The suitable crystals for X-ray analysis were obtained
by recrystallization of the ligand from the mixture of ace-
tone and methanol (1:1 v/v).
FT-IR spectrometer with a KBr disc. H and 13C NMR
1
spectra were obtained using a Varian Gemini 200 spec-
trometer. Electronic spectra were recorded on a Secomam
(Anthelie 2, Advanced, for the range 270–900 nm) and on
a Thermo Nicolet instrument (NEXUS 670 FT-IR, for
the range 900–1400 nm) in (1–2) · 10À3 mol dmÀ3 DMF
solutions of the ligand and complex. Thermal analysis
in argon and air gas carriers with a 15 dm3/min flow-
ing rate and a heating rate of 10 K/min were carried out
using a DuPont 1090 TA system. For thermogravimetric
Anal. Calc. for C17H15N5S: C, 63.53; H, 4.70; N, 21.79.
Found: C, 63.75; H, 4.62; N, 21.55%. UV–Vis spectra
(cmÀ1/loge): 31950 (4.0); ꢀ30000 (4.0).

V.M. Leovac et al. / Polyhedron 26 (2007) 3783–3792
3785
˚
measurements platinum crucible was employed. DSC
curves were recorded in open aluminum sample pans. As
a reference an empty pan was used. The sample masses
were about 5 mg.
lated C–H and N–H distances were 0.93 and of 0.86 A
respectively, and the isotropic displacement parameters
are equal to 1.5 and 1.2 times of the equivalent isotropic
displacement parameters of the C and N atoms. The soft-
ware used for the publication are: PLATON [22], WinGX
[23], PARST [24] and ORTEPIII [25]. Crystal and structure
refinement data for Ph2PzTSC and [Ni(Ph2PzTSC-H)2]
are summarized in Table 1.
2.5. X-ray data collection and structure refinement
The diffraction data for both compounds were collected
on an Enraf-Nonius CAD4 diffractometer [19] by using
˚
graphite-monochromated Mo Ka (0.71073 A) radiation
3. Results and discussion
at 293(2) K. The data were corrected for Lorentz and
polarization effects [20]. Cell constants and the orientation
matrix for data collection, obtained from 25 centered
reflections in the h range of 13.17–15.81ꢁ for the ligand,
corresponded to an orthorhombic cell. In the case off the
complex, the 25 centered reflections in the h range 13.97–
17.25ꢁ led to a triclinic cell. Both structures were solved
by direct methods and difference Fourier methods and
refined on the F2 by full-matrix least-square method [21].
In both cases the all H atoms were determined from DF
maps but at the final stage of the refinement they were
placed at geometrically calculated positions (in purpose
to decrease the number of refined parameters). The calcu-
3.1. Syntheses and general properties of ligand and complex
The title ligand, 1,3-diphenylpyrazole-4-carboxaldehyde
thiosemicarbazone (Ph2PzTSC) was synthesized in good
yield (78%) by condensation from warm ethanolic solu-
tions of the corresponding aldehyde and thiosemicarbazide
in an 1:1 mole ratio, in the presence of a small quantity of
the glacial acetic acid. The white crystals of the ligand are
stable at room temperature. The ligand is very soluble in
Me2CO and DMF, soluble in MeOH, less soluble in aque-
ous EtOH, and practically insoluble in Et2O and water.
The brown single crystals of the cis-square-planar
[Ni(Ph2PzTSC-H)2] complex were obtained by reaction of
the warm methanolic solution of Ni(CH3COO)2 Æ 4H2O
with acetone solution of the ligand in mole ratio of 1:1.
The complex is soluble in DMF, less soluble in Me2CO,
and insoluble in Et2O, MeOH, EtOH, and water.
Table 1
Crystal and structure refinement data for Ph2PzTSC and [Ni(Ph2PzTSC-
H)2]
The ligand participates in coordination with nickel(II)
ion in its monoanionic form after deprotonation of the
hydrazine nitrogen, due to the presence of acetate ion as
a Bro¨nsted base, resulting in complex of non-electrolyte
type. This is in the agreement with its low molar conductiv-
ity. The diamagnetism of the complex is in the accordance
with its square-planar structure confirmed by X-ray analy-
sis. The diamagnetic property of the complex is also
retained in DMF solution.
Empirical formula
Formula weight
Color
Temperature (K)
Crystal size (mm)
Crystal system
Space group
C
321.40
white
17H15N5S
C34H28N20NiS2
699.49
brown
293(2)
293(2)
0.025 · 0.014 · 0.010 0.300 · 0.026 · 0.020
orthorhombic
Pbca
triclinic
ꢀ
P1
Unit cell
˚
a (A)
8.458(4)
17.476(6)
21.986(5)
90
90
90
3249.8(14)
8
1.314
12.364(6)
12.451(5)
12.478(5)
103.27(4)
92.86(6)
115.59(3)
1661.7(12)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3.2. IR spectral studies
3
˚
Volume (A )
A comparative study of the IR spectral data of the com-
plex with that of the ligand gives valuable information
regarding bonding sites of the ligand molecule.
Z
Calculated density, q
1.398
(g cmÀ3
)
The IR spectra of compounds with C@S group attached
to a nitrogen show an absorption band due to m(C@S)
stretching in the region between 1020 and 1250 cmÀ1. In
principle, the ligand can exhibit thione/thiol tautomerism,
since it contains a thioamide NH–C@S functional group
[26]. The missing m(S–H) band between 2600 and
2800 cmÀ1 indicates that the ligand remains in its thione
form. The ligand exhibits a strong band at 1098 and a med-
ium one at 1064 cmÀ1 due to m(C@S) stretches [27]. Also,
two bands at 831 and 807 cmÀ1 in the spectrum of the free
ligand can be attributed to vibrations involving interaction
between m(C@S) stretching and m(C–N) stretchings [28].
The appearance of these bands indicates the existence of
ligand in its thione form in the solid state. The disappear-
h Range for data
collection (ꢁ)
1.58–25.97
2.44–25.98
0.751
Absorption coefficient 0.206
(mmÀ1
F(000)
)
1344
724
Index ranges
0 6 h 6 10,
0 6 k 6 21,
0 6 l 6 27
3617
0 6 h 6 15,
À15 6 k 6 14,
À15 6 l 6 15
6832
Reflections collected
Independent
reflections
Parameters
Goodness-of-fit
R1 [I > 2r(I)]
3617
6511
208
0.914
0.0636
0.273 and À0.241
424
1.004
0.0472
0.383 and À0.338
Largest difference in
peak and hole

3786
V.M. Leovac et al. / Polyhedron 26 (2007) 3783–3792
ance of the m(C@S) band in this region and the appearance
of a medium intensity band at 672 cmÀ1 in the spectrum of
the complex suggests the thioenolization of the C@S group
and coordination of the thiolate sulfur to nickel [29].
In the spectrum of the ligand three bands appear in the
frequency range 3000–4000 cmÀ1. Two of them, at 3327
and 3257 cmÀ1, belong to are due to asymmetrical and
symmetrical m(NH2) stretching, respectively, and one to
the hydrazine m(NH) at 3159 cmÀ1 [30]. The spectral
m(N–H) band of thiosemicarbazone disappears in the com-
plex indicating the deprotonation of the NH group and
coordination via the thiolate sulfur. On the other hand,
the bands in the region attributed to symmetrical and
asymmetrical stretching modes m(NH2) in the spectrum of
the ligand, undergo a change in the spectrum of the com-
plex. This is explained by the coordination of sulfur from
C@S(NH2) group as reported earlier [31,32].
In the ligand spectrum, the strong band observed at
1618 cmÀ1 is assigned to m(C@N) stretching vibrations
[33]. This band shifts to higher wavenumbers at
1626 cmÀ1 in the spectrum of the complex, indicating the
coordination of nitrogen of the azomethine group to the
central metal ion [31,34].
According to the literature data [15,16], IR bands
assigned to m(C@Npz) (pyrazole ring) have been found to
shift to the higher frequency region in the nickel complexes
referring to the participation of the ring nitrogen atom as a
potential bonding site. The negative shift of the very strong
m(C@Npz) frequencies from 1543 cmÀ1 in the spectrum of
the free Ph2PzTSC to 1526 cmÀ1 after complexation with
nickel(II) ion does not indicate the involvement of pyrazole
nitrogen in bonding. This band shifting to lower wavenum-
bers could be explained by resonance effects through the all
conjugated system after the deprotonation and complexa-
tion with nickel(II) ion.
for 3.1 ppm. This behavior of the C-5 pyrazole carbon is
probably caused by the positive resonance effect of the phe-
nyl-substituted pyrazole nitrogen, due to the delocalization
of p-electrons through C-5, C-4, azomethine carbon, and
thiosemicarbazone part of the molecule after the deproto-
nation of hydrazine nitrogen and complexation. Thus,
the reduced electron density of the azomethine carbon after
coordination is compensated by resonance effect which
results in low difference in the chemical shift of the azome-
thine carbon in the spectrum of the free ligand compared to
that in the complex. In this way the electron density of the
azomethine nitrogen is significantly increased as well as its
nucleophility facilitating its coordination to nickel(II). The
practically same d-value for C-3 pyrazole carbon
(139.2 ppm) in the 13C NMR spectrum of the free ligand
compared to the corresponding shift in the complex con-
firms this hypothesis. The chemical shifts of the other car-
bon atoms undergo no significant changes upon
complexation.
1
3.3.2. H NMR spectra
1
The H NMR spectrum of Ph2PzTSC ligand show a
broad singlet at 11.34 ppm relative to the NH next to
C@S, while the signal of the azomethine proton appears
at 9.19 ppm. The sharp singlet of the pyrazole proton
appears at 8.22 ppm while the aromatic protons occur
in 7.38–7.92 ppm range. It is interesting to notice the
presence of two broad singlets for two NH2 protons, at
8.27 and 7.80 ppm respectively. These two protons are
different which means that the free rotation around
C–N bond is hindered because of its partial double bond
character [37].
The coordinating mode of the ligand was confirmed by
1
comparing H NMR spectral data of the ligand with the
corresponding ones in the complex. The absence of the
NH proton signal in the spectrum of the complex suggests
the thioenolization and subsequently, the replacement of a
proton by the metal ion. This replacement with nickel(II)
induces the shift of NH2 protons to lower d-values in the
spectrum of the complex (overlapped with the aromatic
protons shifts in 6.97–7.19 ppm region).
3.3. NMR spectral studies
The assignment of all reported signals (1H and 13C) was
carried out by means of 1D and 2D homo- and heteronu-
clear correlated NMR spectroscopy.
A significant downfield shift of the azomethine proton
signal in the complex (Dd = 0.65 ppm) with respect to the
corresponding free ligand confirms the coordination of
azomethine nitrogen [15,27].
3.3.1. 13C NMR spectra
The carbon C@S signal appears at higher field in the
spectrum of the complex compared to that in the ligand.
This behavior suggests thione-to-thiol evolution in the
ligand, an increase in the thiocarbonyl-deprotonated nitro-
gen bond order [35] and possible coordination of the nickel
ion to the thiolic sulfur atom.
It is interesting to emphasize that C-5 pyrazole proton
shifts to lower d-value from 8.22 ppm in the spectrum of
the ligand to 7.49 ppm in the spectrum of the complex.
On the other hand, the doublet assigned to ortho-N-substi-
tuted phenyl protons at 7.90 ppm (center of doublet) is
shifted to lower field in the spectrum of the complex at
8.03 ppm, together with meta and para protons. These
shifts are induced by positive resonance effect of phenyl-
substituted pyrazole nitrogen and the participation of its
electron pair in the delocalization of p-electrons after coor-
dination, which is in the accordance with 13C NMR spec-
tral data for the free ligand and its nickel complex. The
13C NMR spectrum shows an unexpectedly low positive
Dd = d(complex) À d(free ligand) shift of only 2.0 ppm for
the azomethine carbon. In the earlier reports, the complex-
ation through azomethine nitrogen causes a great positive
chemical shift of the azomethine carbon in the 13C NMR
spectra of complexes [35,36]. On the other side, the C-5
pyrazole carbon exhibits
15.0 ppm, while the C-4 carbon is shifted to higher field
a great positive shift of

V.M. Leovac et al. / Polyhedron 26 (2007) 3783–3792
3787
Table 2
other aromatic proton shifts of the ligand and those in the
complex appear in the expected region.
˚
Selected bond lengths (A) and angles (ꢁ)
Ph2PzTSC
[Ni(Ph2PzTSC-H)2]
A
3.4. Electronic spectra
B
Ni1–N1
Ni1–S1
1.914(3)
2.141(2)
1.921(3)
2.148(2)
Similarly to the ligand, the red-brownish DMF solution
of the Ni(II) complex absorbs in the UV range in several
unresolved bands belonging to intraligand transitions. A
shoulder appearing at about 25500 cmÀ1 is probably CT
band.
N1–N2
C1–N2
C1–N3
C1–S1
C2–N1
C2–C3
N4–C5
C5–C12
1.387(5)
1.344(6)
1.315(6)
1.692(5)
1.279(6)
1.453(7)
1.432(7)
1.483(7)
1.424(4)
1.289(5)
1.352(5)
1.744(4)
1.282(4)
1.449(5)
1.438(5)
1.470(5)
1.410(4)
1.304(4)
1.349(4)
1.737(4)
1.296(4)
1.446(5)
1.435(5)
1.463(5)
The only one d–d band at about 19000 cmÀ1 appearing
as a shoulder of this CT band is consistent with the
assumption of a preserved square-planar geometry in
DMF solution. In the near IR region, under 10000 cmÀ1
no bands were observed, as is usual in complexes with this
geometry [38].
N1–Ni1–S1
Ni1–N1–C2
Ni–N1–N2
Ni–S1–C1
86.1(2)
128.3(3)
117.7(2)
94.4(2)
85.51(9)
130.8(2)
118.3(2)
95.1(2)
3.5. Crystal structures
N1a–Ni–N1b
S1a–Ni–S1b
N1a–Ni–S1b
N1b–Ni–S1a
102.5(2)
90.1(1)
162.9(3)
163.8(3)
3.5.1. Crystal structure of Ph2PzTSC
Fig. 2. shows an ORTEP plot of Ph2PzTSC ligand with
the atomic numbering scheme. Relevant bond distances
and angles are listed in Table 2. The thiosemicarbazone
moiety of the ligand shows E configuration around the
C2–N1 and C1–N2 bond as found in most of the thiose-
micarbazones. As confirmed by the C@S bond distance
N2–N1–C2
N1–C2–C3
N1–N2–C1
N2–C1–S1
N2–C1–N3
N5–N4–C6
N5–C5–C12
114.3(5)
113.9(3)
124.3(3)
110.9(3)
123.9(3)
119.4(4)
120.5(3)
119.4(4)
110.8(3)
127.6(3)
111.4(3)
122.9(3)
118.3(3)
120.2(3)
121.3(3)
119.0(5)
119.7(4)
119.7(4)
117.4(4)
119.5(5)
118.4(5)
˚
of 1.692(5) A, the ligand is present in its thione form.
The partial double bond characters in formally single
bonds of thiosemicarbazone moiety suggest the extensive
electron delocalization. Consequently, this part of molecule
exhibits considerable planarity. The moiety comprising C2,
N1, N2, C1, S1, and N3 atoms has a mean plane deviation
of the molecule allows its free rotation, thus the dihedral
angle formed between the best planes of the thiosemicarba-
zone fragment and the central pyrazole ring achieves 48.3ꢁ.
The bond lengths within the aromatic parts of the mol-
ecule are normal [39]. The phenyl rings are titled in the
same direction relative to the central pyrazole moiety.
The dihedral angles formed between the best planes of
the pyrazole and the two phenyl rings are similar, 18.1ꢁ
and 19.1ꢁ with the C6–C11 and C12–C17 rings respectively.
The dihedral angle between the titled phenyls is 6.0ꢁ.
The three intramolecular hydrogen bonds of the very
bent character (D–HÁ Á ÁA ꢁ 100ꢁ) stabilize the geometry
of Ph2PzTSC (Table 3). The strongest intermolecular
N3–H3Á Á ÁN5 hydrogen bond connects the centrosym-
metrically related molecules into the cyclic dimers. Since
this interaction is formed between the thiosemicarbazone
and pyrazole moieties it probably causes the above men-
tioned twisting of the thiosemicarbazone fragment. The
two interactions of the N–HÁ Á ÁS type (Table 3) further
connect the molecules of the ligand into the 2D struc-
tures parallel to the ac crystallographic plane. The seg-
ment of this 2D hydrogen bonded pattern is shown in
Fig. 3.
˚
of 0.036 A with the N1 showing the greatest displacement
˚
˚
of 0.082 A. The formally single C2–C3 bond (1.453(7) A)
which connects the thiosemicarbazone fragment to the rest
C9
C10
C8
C11
C7
C6
N4
N3
C4
N1
N2
C3
N5
C1
S1
C2
C5
C12
C17
C13
C14
C16
C15
3.5.2. Crystal structure of [Ni(Ph2PzTSC-H)2]
In [Ni(Ph2PzTSC-H)2] complex the Ni(II) ion lies in an
approximately square-planar coordination environment
formed by two hydrazine N1 and two thiol S1 atoms from
Fig. 2. Crystal structure of Ph2PzTSC with the atomic numbering scheme.
Ellipsoids are drawn at the 50% probability level.

3788
V.M. Leovac et al. / Polyhedron 26 (2007) 3783–3792
Table 3
Geometry of hydrogen bonds
coordination. The most significant difference is found in
the C–S bond which increases its length upon the ligand
˚
˚
˚
˚
D–HÁ Á ÁA
Ph2PzTSC
D–H (A) HÁ Á ÁA (A) DÁ Á ÁA (A) D–HÁ Á ÁA (ꢁ)
complexation for an average value of 0.048 A. On the con-
trary, C1–N2 bond decreases its length for the similar aver-
age value.
N3–H3aÁ Á ÁN1i
C7–H7Á Á ÁN5i
C17–H17Á Á ÁN5i
N3–H3aÁ Á ÁN5ii
N2–H2nÁ Á ÁS1iii
N3–H3bÁ Á ÁS1iv
0.86
0.93
0.93
0.86
0.86
0.86
2.29
2.48
2.53
2.31
2.68
2.63
2.642(2)
2.801(2)
2.836(2)
3.079(2)
3.312(4)
3.421(3)
104.7(3)
100.1(4)
99.8(4)
140.1(3)
131.1(5)
155.2(5)
Five membered chelate rings assume envelope confor-
˚
mation (the puckering parameters are: q2 = 0.324(3) A,
˚
/2 = 181.0(7)ꢁ, q2 = 0.320(2) A, /2 = 182.5(7)ꢁ for the
branches A and B respectively) and form the dihedral angle
of 20.4ꢁ. The thiosemicarbazide moiety upon complexation
retains its planarity, however it is worth mentioning that
the dihedral angle between its best plane and central pyra-
zole ring decrease from the value of 48.3ꢁ to the values of
19.2ꢁ and 16.9ꢁ in the A and B branch respectively. This
change in the ligand geometry is probably caused by the
[Ni(Ph2PzTSC-H)2]
C7a–H7aÁ Á ÁN5av
C7b–H7bÁ Á ÁN5bv
0.93
0.93
2.57
2.54
2.61
2.67
2.14
2.12
2.853(2)
2.830(2)
2.883(2)
2.930(2)
3.003(3)
2.968(2)
98.2(3)
98.5(3)
97.5(3)
93.6(3)
178.3(3)
168.9(3)
C17a–H17aÁ Á ÁN5av 0.93
C17b–H7bÁ Á ÁN5bv
N3a–H3aÁ Á ÁN2avi
N3b–H3bÁ Á ÁN2bvii
0.93
0.86
0.86
Symmetry codes: (i) x, y, z; (ii) Àx + 2, Ày, Àz + 2; (iii) x + 1.5, y,
Àz + 2.5; (iv) x + 0.5, y, Àz + 2.5; (v) x, y, z; (vi) Àx, Ày, Àz + 2;
(vii) Àx + 1, Ày, Àz + 1.
C16a
C15a
C17a
the deprotonated thiosemicarbazone ligands (Fig. 4). The
molecules of L have the cis mutual arrangement. The four
donor atoms are significantly displaced from the mean
coordination plane with the maximum deviation of atom
C14a
C7a
C13a
C12a
C5a
N1b
N5a
C8a
˚
N1a (0.471 A).
C6a
C3a
The deviation from the regular square-planar geometry
is also indicated by the coordination angles (Table 2).
The N1a–Ni–N1b angle of 102.5(2)ꢁ shows significant dis-
agreement with the theoretical value (90ꢁ) probably due to
the steric effects between the bulky fragments attached to
N1 atoms. The S1a–Ni–S1b angle shows almost ideal value
of 90.1(1)ꢁ. The coordination bond distances Ni–N and
Ni–S are comparable to those found in similar neutral
square-planar complexes of Ni(II). Comparison of the
remaining bonds in [Ni(Ph2PzTSC-H)2] to those of the
uncoordinated ligand Ph2PzTSC shows marked differences
probably originated by the ligand’s deprotonation and
N4a
C4a
C9a
C11a
C2a
C10a
N2a
C1a
N2b
N1a
Ni1
C1b
N3a
N3b
S1a
S2
Fig. 4. Crystal structure of [Ni(Ph2PzTSC-H)2] with the atomic number-
ing scheme (the atomic numbering in the branch B is equivalent to A and
is partly excluded for the sake of clarity). Ellipsoids are drawn at the 50%
probability level.
Fig. 3. View of the 2D hydrogen bonding linkage in Ph2PzTSC.

V.M. Leovac et al. / Polyhedron 26 (2007) 3783–3792
3789
H11a
C11a
Cg(1)
N2a
H3a
N2b
H3b
N3a
N3b
a
c
Fig. 5. Segment of the 2D molecular arrangement in [Ni(Ph2PzTSC-H)2].
R2
R2
braking of the N3–H3Á Á ÁN5 hydrogen bond, which plays a
key role in the ligand’s crystal arrangement. In the mole-
cule of complex, the atom N5 remains only as an acceptor
in the two intramolecular C–HÁ Á ÁN bonds also present in
the molecule of the free ligand (Table 3).
R3
N
N
R3
N
N
N
S
N
N
S
R1
R1
R1
N
N
S
S
The molecules of complex are interconnected by the two
pairs of N–HÁ Á ÁN hydrogen bonds acting on each side of
the molecule and connecting the [Ni(Ph2PzTSC-H)2] into
the chains parallel to the diagonal of the ac plane. There
is no further hydrogen bonding in this crystal structure;
however the arrangement of the bulky carbonyl fragments
provides the additional stabilizing contacts of the C–HÁ Á Áp
Ni
Ni
R1
N
N
R3
N
R3
R2
R2
i
˚
type (C13a–H13aÁ Á ÁCg(1) : H13aÁ Á ÁCg = 2.92 A, C13a–
H13aÁ Á ÁCg = 140.1ꢁ; C11a–H11aÁ Á ÁCg(2)ii: H11aÁ Á ÁCg =
Fig. 6. Bis (bidentate) cis- and trans-Ni(II) complexes with thiosemicar-
iii
˚
bazide-based ligands.
2.88 A, C11a–H11aÁ Á ÁCg = 137.1ꢁ; C17b–H17bÁ Á ÁCg(1) :
˚
H17bÁ Á ÁCg = 2.99 A, C17b–H17bÁ Á ÁCg = 102.3ꢁ. Cg(1)
and Cg(2) are the centers of the rings N4b–C5b and
C12a–C17a respectively. Symmetry codes: (i) x, y, z; (ii):
Àx + 1, Ày, Àz + 2; (iii) Àx, Ày À 1, Àz + 1). It is interest-
ing to notice that the dihedral angles formed between the
central pyrazole moiety and the phenyl rings increase, com-
pared to the corresponding angles in the ligand molecule
(from 18.1ꢁ and 19.0ꢁ in HL to 27.0ꢁ and 27.2ꢁ (branch
A) and 26.2ꢁ and 27.2ꢁ (B branch) of [Ni(Ph2PzTSC-H)2]
respectively). However, in contrast to the branch B where
the phenyl rings are as in the case of the ligand titled in
the same direction regarding the pyrazole ring (the dihedral
angle between the phenyls is 16.7ꢁ), in the A branch the
phenyl rings are titled in the mutually opposite directions
regarding the pyrazole (the dihedral angle between the phe-
nyls is 49.3ꢁ). Namely, the C6a–C11a phenyl has the orien-
tation which is different from those present in the free
ligand and the branch B. It appears that in the absence
of the other intermolecular interactions the C11a–HÁ Á Áp
interaction in which this phenyl is involved has the decisive
role in its final orientation. The segment of the 2D molec-
ular arrangement is given in Fig. 5.
3.5.3. Comparative database study of the similar
bis(bidentate) Ni(II) complexes with the
thiosemicarbazide-based ligands
As the X-ray analysis of [Ni(Ph2PzTSC-H)2] has shown,
the square-planar geometry of this complex is rather tetra-
˚
hedrally deformed (NNSS donor atoms deviate for 0.27 A
in average from the mean plane defined with these atoms).
To compare its structural parameters and the coordination
geometry to those of the similar bis(bidentate) Ni(II) com-
plexes with the thiosemicarbazide-based ligands (Fig. 6) the
CSD [40] search has been included. There are 37 crystal
structures with the coordination number four extracted
from the CSD and their refcodes are listed in Table 4.1
The fact that only one (NIEPZF) of these structures shows
the tetrahedral arrangement of the ligands can be explained
by known preference of the Ni(II) ions to form square-pla-
nar complexes. From the remaining crystal structures, only
1
List of references for all crystal structures extracted from CSD is given
in the Supplementary material.

3790
V.M. Leovac et al. / Polyhedron 26 (2007) 3783–3792
Table 4
each of the listed complexes, we have analyzed the values
of the dihedral angles formed between two N–Ni–S best
planes. In Table 4. this angle is assigned as P1/P2. Because
the N–Ni–S planes contain the central metal ion and a
whole set of the donor atoms, the angle between them is
sufficient to define the degree of the deformation of the
coordination geometry from the ideal square-planar (P1/
P2 = 0ꢁ) toward the tetrahedral one (P1/P2 = 90ꢁ). The
structures in Table 4 are sorted with the reference to P1/
P2 parameter. According to it the greatest deformations
from the regular square-planar geometry are found in the
complexes with the cis-positioned voluminous ligands as
it is the case in the novel [Ni(Ph2PzTSC-H)2] which is the
second most deformed. Interesting is the case of QEBDAC
structure which exhibits somewhat less deformed square-
planar geometry (P1/P2 parameter) but the most deformed
chelate rings (based on parameters Ni_P3 and Ni_P4 which
represent the displacement of the Ni atom from the best
planes of the rest of the chelate rings). These observations
suggest that there are two ways in which the geometry of
the cis-Ni(II) square-planar complexes adopts to the
requirements of the voluminous ligands: (1) through the
distortion of the coordination geometry around the metal
ion; (2) through the deformation of the preferentially pla-
nar five membered chelate rings.
Selected geometrical parameters for four-coordinated Ni(II) complexes
with bidentate thiosemicarbazide-based ligands
Refcodea
P1/P2 (ꢁ)
Ni_P3 (A)
Ni_P4 (A)
˚
˚
NIEPZF
75.5
0.170
0.171
cis
JEYPOS*
24.6
22.7
20.6
19.5
12.7
6.6
5.8
1.1
0.2
0.2
0.639
0.602
0.717
0.591
0.723
0.093
0.759
0.010
0.112
0.027
0.629
0.596
0.573
0.621
0.764
0.093
0.758
0.010
0.074
0.027
[Ni(Ph2PzTSC-H)2]*
XARWOC*
QEBDEG*
QEBDEG*
NIDTSS10
QEBDAC*
CNITSC
ALAHIE
WERNIQ
trans
WUHQEV
XENNIN
BAKBUL
TCARNI01
EHAZOC
KUXLEU
ABECOA
ZOJXIF
BAKBIZ
RONDUT
WABHOX
BAKBOF
FIBWIX
TCARNI
FUTRAN
NIDTSS10
NIPTCZ10
BAKBEV
HOPCEU
VOGVIW
EHAZUI
EBEHEZ
KOMGAU
QOVGAJ
NSEMSU
ABECOA
FACKIE
IHAXAQ
TIFTUX
TNITSC
4.2
3.9
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.491
0.249
0.295
0.213
0.409
0.232
0.108
0.089
0.219
0.419
0.277
0.133
0.205
0.198
0.191
0.061
0.008
0.170
0.386
0.292
0.146
0.351
0.512
0.272
0.002
0.133
0.569
0.445
0.281
0.282
0.191
0.162
0.297
0.213
0.409
0.232
0.108
0.089
0.219
0.419
0.277
0.133
0.205
0.198
0.191
0.061
0.008
0.170
0.386
0.292
0.146
0.351
0.512
0.272
0.002
0.133
0.569
0.445
0.281
0.282
It is evident that the trans-complexes have more regular
square-planar geometry which is reflected in very low val-
ues of the P1/P2 parameter (Table 4) with NNSS donor
atoms being practically in coplanar position. If voluminous
substituents in these complexes exist they are also in trans
position and from that reason they are not able to form
intramolecular steric interactions. It seems however that
in some cases (KOMGAU and FACKIE) they still affect
the chelate rings conformation.
3.6. Thermal analysis
The decomposition curves of Ph2PzTSC refer to the
melting of the compound which is accompanied by its
decomposition with an onset temperature of 490 K
(217 ꢁC). The fragmentation steps are superposed avoiding
thus the determination of the decomposition mechanism.
Some coke residue is observed in argon above 1000 K.
The decomposition of [Ni(Ph2PzTSC-H)2] begins at the
same temperature (490 K) as that of the ligand with a low
mass loss of about 2% (repeated measurements with sam-
ples from different synthesis). This means that the complex
formation does not raise the thermal stability of the com-
pound as is usual. On the basis of the mass loss, taking
into account the short range interactions in the crystal,
the leaving fragment is most probable an ammonia mole-
cule (Calc. 2.4%). In IR spectrum of the intermediate the
band of the original complex, assigned to m(NH2) vibra-
tion, has almost completely vanished, supporting the
proposition of the departure of an ammonia molecule dur-
ing the thermal decomposition up to 520 K. The deep pur-
ple color of the complex has also changed to dark brown.
The complexes with the cis-positioned voluminous ligands are labeled by
asterisk (*).
a
List of references for all crystal structures extracted from CSD is given
in the Supplementary material.
eight show the cis mutual arrangement (Fig. 6a) of the
bidentate ligands, suggesting that this configuration is gen-
erally less favorable than trans (Fig. 6b). As expected, due
to the steric hindrance the interligand N–Ni–N angle is lar-
ger in the cis-complexes with bulky carbonyl moieties
attached to N donor atoms and it is ranging from 99.7ꢁ
to 103.8ꢁ. Corresponding geometrical parameters calcu-
lated for [Ni(Ph2PzTSC-H)2] correlate very well with these
values.
To compare the extent of the tetrahedral distortion on
the same level (from the ideal square-planar geometry) in

V.M. Leovac et al. / Polyhedron 26 (2007) 3783–3792
3791
Appendix A. Supplementary material
CCDC 633472 and 633473 contain the supplementary
crystallographic data for Ph2PzTSC and [Ni(Ph2PzTSC-
H)2]. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from
the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data associated with this article can be found in the online
version, at doi:10.1016/j.poly.2007.04.012.
References
[1] D.L. Klayman, J.F. Bartosevich, T.S. Griffin, C.J. Mason, J.P.
Scovill, J. Med. Chem. 22 (1979) 855.
[2] D.X. West, S.B. Padhye, P.B. Sonawane, Struct. Bond. 76 (1991) 1.
[3] A.E. Liberta, D.X. West, Biometals 5 (1992) 121.
[4] F.A. French, E.J. Blanz, J.R. Do Amaral, D.A. French, J. Med.
Chem. 13 (1970) 1117.
[5] H. Beraldo, D. Gambino, Mini. Rev. Med. Chem. 4 (2004) 31.
[6] W.L. John, R.M. Patera, M.J. Plummer, B.P. Halling, D.A. Yuhas,
Pest. Sci. 42 (1994) 29.
[7] M.J. Genin, C. Biles, B.J. Keiser, S.M. Poppe, S.M. Swaney, W.G.
Tarplay, Y. Yagi, D.L. Romero, J. Med. Chem. 43 (2000) 1034.
[8] H. Hashimoto, K. Imamura, J.I. Haruta, K. Wakitani, J. Med. Chem.
45 (2002) 1511.
[9] A.G. Habeeb, P.N.P. Rao, E.E. Knaus, J. Med. Chem. 44 (2001)
3039.
[10] M.L.P. Price, W.L. Jorgensen, J. Am. Chem. Soc. 122 (2000) 9455.
[11] R.R. Ranatunge, R.A. Earl, D.S. Garvey, D.R. Janero, L.G. Letts,
A.M. Martino, M.G. Murty, S.K. Richardson, D.J. Schwalb, D.V.
Young, I.S. Zemtseva, Bioorg. Med. Chem. Lett. 14 (2004) 6049.
[12] E. Elzein, R. Kalla, X. Li, T. Perry, E. Parkhill, V. Palle, V.
Varkhedkar, A. Gimbel, D. Zeng, D. Lustig, D. Leung, J. Zablocki,
Bioorg. Med. Chem. Lett. 16 (2006) 302.
[13] D.X. West, A.E. Liberta, S.B. Padhye, R.C. Chikate, P.B. Sonawane,
A.S. Kumbhar, R.G. Yerande, Coord. Chem. Rev. 123 (1993) 49.
[14] A.K. Barik, S. Paul, S.K. Kar, R.J. Butcher, J.C. Bryan, Polyhedron
18 (1998) 571.
[15] N.C. Saha, R.J. Butcher, S. Chaudhuri, N. Saha, Polyhedron 22
(2003) 383.
[16] N.C. Saha, R.J. Butcher, S. Chaudhuri, N. Saha, Polyhedron 24
(2005) 1015.
[17] D.D. Perrin, W.L.F. Armarego, D.R. Perrin, Purification of Labo-
ratory Chemicals, second ed., Pergamon Press, Oxford, 1980.
[18] P. Rathelot, N. Azas, H. El-Kashef, F. Delmas, C. Di Giorgio, P.
Timon-David, J. Maldonado, P. Vanelle, Eur. J. Med. Chem. 37
(2002) 671.
Fig. 7. Thermal decomposition curves of [Ni(Ph2PzTSC-H)2].
The mass loss is accompanied with an endothermic DSC
peak which is followed by an exothermic one in a temper-
ature range of 510–530 K. For this DSC peak no corre-
sponding DTG peak is observed (see Fig. 7). Namely, in
510–560 K temperature range DTG curve falls to zero
referring to formation of a stable intermediate. The exo-
thermic process may be the consequence of a spontaneous
intra- or intermolecular rearrangement [41], due to the loss
of NH3 molecule. According to the observation with a
hot-stage microscope, there is no melting of the intermedi-
ate up to 550 K. The melting with an onset temperature at
550 K is immediately followed by an exothermic
decomposition.
The decomposition of the complex begins at somewhat
higher temperature in air, being continuous above 560 K
in both atmospheres (Fig. 7). There is no possibility thus
to determine the decomposition mechanism. As in sulfur
containing complexes in air, in a platinum crucible, uncon-
trollable oxidation processes are taking place [42,43], it is
meaningless to analyze the composition of the residue. In
argon the decomposition is not finished up to 1000 K.
[19] Enraf-Nonius CAD4 Software, Version 5.0, Enraf-Nonius, Delft, The
Netherlands, 1989.
[20] CAD-4 Express Software. Enraf-Nonius, Delft, The Netherlands,
1994.
[21] (a) G.M. Sheldrick, SHELXS97. Program for the Solution of Crystal
Structures, University of Go¨ttingen, Germany, 1997;
(b) G.M. Sheldrick, SHELXL97. Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Germany, 1997.
[22] (a) A.L. Spek, Acta Crystallogr., Sect. A 46 (1990) C34;
(b) A.L. Spek, PLATON, A Multipurpose: Crystallographic Tool,
Utrecht University, Utrecht, The Netherlands, 1998.
[23] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.
[24] M. Nardelli PARST, J. Appl. Crystallogr. 28 (1995) 659.
[25] L.J. Farrugia ORTEPIII for Windows, J. Appl. Crystallogr. 30 (1997)
565.
Acknowledgments
This work was supported by the Ministry of Science and
Environmental Protection of the Republic of Serbia (Pro-
ject No. 142028B) and the Provincial Secretariat for Sci-
ence and Technological Development of Vojvodina.
[26] Y. Tian, C. Duan, C. Zhao, X. You, Inorg. Chem. 36 (1997) 1247.

3792
V.M. Leovac et al. / Polyhedron 26 (2007) 3783–3792
[27] M.R. Maurya, A. Kumar, M. Abid, A. Azam, Inorg. Chim. Acta 359
(2006) 2439.
[28] R.M. Silverstein, C.G. Bassler, T.C. Morrill, Spectrometric Identifi-
cation of Organic Compounds, third ed., John Wiley and Sons Inc.,
New York, 1974, p. 113.
[35] J.S. Casas, M.C. Rodriguez-Arguelles, U. Russo, A. Sanchez, J.
¨
Sordo, A. Vazquez-Lopez, S. Pinelli, P. Lunghi, A. Bonati, R.
Albertini, J. Inorg. Biochem. 69 (1998) 283.
[36] M.R. Maurya, A. Kumar, A.R. Bhat, A. Azam, C. Bader, D. Rehder,
Inorg. Chem. 45 (2006) 1260.
[29] P. Bera, N. Saha, S. Kumar, D. Banerjee, R. Bhattacharya,
Transition Met. Chem. 24 (1999) 425.
[37] M. Belicchi Ferrari, A. Bonardi, G. Gaspari Fava, C. Pelizzi, P.
Tarasconi, Inorg. Chim. Acta 223 (1994) 77.
[30] M.B. Ferrari, S. Capacchi, G. Reffo, G. Pelosi, P. Tarasconi, R.
Albertini, S. Pinelli, P. Lunghi, J. Inorg. Biochem. 81 (2000) 89.
[31] P. Bindu, M.R.P. Kurup, T.R. Satyakeerty, Polyhedron 18 (1999)
321.
[38] A.B.P. Lever, Inorganic Electronic Spectroscopy, Russian Edition.,
Mir, Moscow, 1987, p. 2.
[39] M. Dincer, N. Ozdemir, I. Yildirim, E. Demir, Y. Akcamur, S. Isik,
Acta Crystallogr., Sect. E 60 (2004) o317.
[32] E.M. Jouad, M. Allain, M.A. Khan, G.M. Bouet, Polyhedron 24
(2005) 327.
[40] F.H. Allen, Acta Crystallogr., Sect. B 58 (2002) 380.
[41] H.A. El-Boraey, J. Therm. Anal. Cal. 81 (2005) 339.
ˇ
´
´
´
´
´
´
[33] E.M. Jouad, M. Allain, M.A. Khan, G.M. Bouet, J. Mol. Struct. 604
(2002) 205.
[42] K. Meszaros Szecsenyi, V.M. Leovac, Z.K. Jacimovic, G. Pokol, J.
Therm. Anal. Cal. 74 (2003) 943.
´ ´ ´
´ ´
[34] M. Rodriguez-Arguelles, M.B. Ferrari, G.G. Fava, G. Pelizzi, G.
¨
[43] A. Kovacs, D. Nemcsok, G. Pokol, K. Meszaros Szecsenyi, V.M.
ˇ
´ ´ ´
Leovac, Z.K. Jacimovic, I. Radosavljevic Evans, J.A.K. Howard,
Pelosi, R. Albertini, A. Bonati, P.P. Dall’ Aglio, P. Lunghi, S. Pinelli,
J. Inorg. Biochem. 66 (1997) 7.
´
Z.D. Tomic, G. Giester, New J. Chem. 29 (2005) 833.