Transition metal complexes with pyrazole based ligands, part 15. Cobalt(iii)-, nickel(ii)- and copper(ii)-complexes with 3,5-dimethyl-1-thiocarboxamidepyrazole

Article abstract of DOI:10.1023/B:JTAN.0000011026.41481.bd

The complex formation of cobalt(II)-, nickel(II) and copper(II) sulphate hydrates with 3,5-dimethyl-1-thiocarboxamidepyrazole (HL) was studied. The influence of the anions on the course of the reaction was also examined, using nickel(II) salts with various anions. Beside the NiSO₄.7H ₂O the reaction has been carried out with Ni(OAc)₂, Ni(CF₃COO)₂ and Ni(SCN)₂, Compounds with the following composition were obtained: Co(L)₃, Ni(L)₂ and [Cu(SCN)L]₂. The structure of the ligand and the Co(L)₃ complex was determined by single crystal X-ray analysis, while that of the Ni(L)₂ was solved by analysis of powder diffraction X-ray data, The most probable structure of the copper(II) complex is proposed on the basis of the elemental analyses data, FT-IR spectrometry and magnetic measurement. The thermal decomposition of the complexes was investigated by thermogravimetry, DSC and coupled TG-MS measurements. In the case of the nickel(II) compound, a relatively stable intermediate was detected in the 550-650 K temperature range. The composition of the intermediate, Ni(SCN)(NCS), was determined by FT-IR-spectrometry.

Full text of DOI:10.1023/B:JTAN.0000011026.41481.bd

Journal of Thermal Analysis and Calorimetry, Vol. 74 (2003) 943–952
TRANSITION METAL COMPLEXES WITH
PYRAZOLE BASED LIGANDS
Part 15. Cobalt(III)-, nickel(II)- and copper(II)-complexes
with 3,5-dimethyl-1-thiocarboxamidepyrazole
1
*
1
2
3
K. Mészáros Szécsényi , V. M. Leovac , ¦. K. Jaºimoviº and G. Pokol
1
University of Novi Sad, Faculty of Sciences, Institute of Chemistry, 21000 Novi Sad,
Trg D. Obradoviºa 3, Yugoslavia
2
Faculty of Metallurgy and Technology, Podgorica, Yugoslavia
3
Institute for General and Analytical Chemistry, Budapest University of Technology and Economics,
1521 Budapest, Hungary
(Received April 3, 2003; in revised form October 7, 2003)
Abstract
The complex formation of cobalt(II)-, nickel(II) and copper(II) sulphate hydrates with 3,5-dimethyl-
1
-thiocarboxamidepyrazole (HL) was studied. The influence of the anions on the course of the reaction
was also examined, using nickel(II) salts with various anions. Beside the NiSO ·7H O the reaction has
been carried out with Ni(OAc) , Ni(CF COO) and Ni(SCN) . Compounds with the following compo-
sition were obtained: Co(L) , Ni(L) and [Cu(SCN)L] . The structure of the ligand and the Co(L)
complex was determined by single crystal X-ray analysis, while that of the Ni(L) was solved by anal-
4
2
2
3
2
2
3
2
2
3
2
ysis of powder diffraction X-ray data. The most probable structure of the copper(II) complex is pro-
posed on the basis of the elemental analyses data, FT-IR spectrometry and magnetic measurement.
The thermal decomposition of the complexes was investigated by thermogravimetry, DSC and
coupled TG-MS measurements. In the case of the nickel(II) compound, a relatively stable intermedi-
ate was detected in the 550–650 K temperature range. The composition of the intermediate,
Ni(SCN)(NCS), was determined by FT-IR-spectrometry.
Keywords: cobalt(III)-, nickel(II) and copper(II) complexes, 3,5-dimethyl-1-thiocarboxamidepyrazole,
FT-IR-spectrometry, thermal analysis
Introduction
Some natural products like distamycin A [1, 2] show a wide spectrum of antiviral and
antitumor activities. Monopyrazole analogues of distamycin A display antiviral ef-
fect comparable to that of distamycin A [3].
The complexing ability of pyrazole derivatives is well known [4–6]. They are
applied for the metal ion extraction [5], used in pharmaceutical industry as drug com-
*
Author for correspondence: E-mail: mszk@im.ns.ac.y
1
388–6150/2003/ $ 20.00
Akadémiai Kiadó, Budapest
©
2003 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

9
44
MÉSZÁROS SZÉCSÉNYI et al.: TRANSITION METAL COMPLEXES
ponents, or components of herbicides and antifungal agents [7]. The azo-derivatives
of the pyrazoles are important pigments for the synthetic leader and vinyl poly-
mers [8], therefore their thermal stability is of great importance.
The active site of metall-proteins may be partly mimicked by simple models
containing pyrazole ring which similarity in the electronic and steric sense to
imidazoles, as parts of the histidine fragments of proteins [9], is significant but the
former compounds are more readily synthesized. Recently, attention is paid to the de-
sign of various pyrazole ligands with special structural properties to fulfill the spe-
cific stereochemical requirements of a particular metal-binding site [10].
A monodentate coordination of the pyrazole derivatives is established through
its pyridine nitrogen atom. The deprotonated pyrazole, the pyrazolide ion, can coordi-
nate through both nitrogen atoms as a bidentate ligand. When the pyrazole ring has
substituents with different donor atoms in position 1-, 3- or 5-, it can act as bridging
or non-bridging polydentate ligand [11–15].
The aim of our systematic studies on transition metal pyrazole complexes is to
investigate the influence of the pyrazole ring substituents on the course of the com-
plex formation [16–18]. In this paper we have examined the reaction of cobalt(II)-,
nickel(II) and copper(II) sulphate hydrates with 3,5-dimethyl-1-thiocarboxamide-
pyrazole (HL). The obtained compounds were Co(L) , Ni(L) and [Cu(SCN)L] .
3 2 2
Complexes of the former cations with analogues ligands, namely, with 3,5-di-
methyl-1-N-methyl and 1-N-ethyl thiocarboxamidepyrazole are already known and
structurally characterized [19, 20]. The structure of the 3,5-dimethyl-1-thiocarbox-
amidepyrazole ligand [21] as well as the structure of the Co(L) , obtained by the reac-
3
tion of cobalt(II) acetate instead of cobalt(II) sulfate with the same ligand, has been
determined by single crystal X-ray analysis [22]. Since the role of the anions in the
reaction cannot be ruled out, we have used different nickel(II) salts to examine the in-
fluence of the anions on the complex formation. The complex formation has been car-
ried out beside NiSO also with Ni(Oac) , Ni(SCN) and Ni(CF COO) . As a result,
4 2 2 3 2
the same Ni(L) complex was formed. The thermal stability of the compounds has
2
been studied by thermogravimetry and DSC. For the better understanding of the ther-
mal decomposition mechanism, the TG-equipment is often is combined with instru-
ments for EGA [23]. In our case the TG was combined with MS.
Experimental
All chemicals used were reagent grade
The ligand was prepared by the reaction of thiosemicarbazide (5 g) and acetyl ace-
3
3
3
tone (5 cm ) in acidic aqueous solution (250 cm H O+1 cm cc. HCl) at room tem-
2
perature. Reaction time: 6 h. The white precipitate was washed with water and dried
at room temperature.
The complexes were synthesised by mixing of cold methanolic solutions of the
appropriate metal(II) sulphate hydrate (1 mmol metal salt) and the ligand (2.5 mmol).
3
The total volume of the solution after mixing was about 10 cm . As the solubility of
J. Therm. Anal. Cal., 74, 2003

MÉSZÁROS SZÉCSÉNYI et al.: TRANSITION METAL COMPLEXES
945
CuSO ⋅5H O in methanol is very low, a saturated aqueous solution of the copper(II)
4
2
sulphate was used instead of its solution in methanol. The reaction mixture was
slightly heated about 10 min. In the case of the copper(II) compound an immediately
precipitation was observed, while the other two compounds precipitated in 30 min.
The obtained complexes were filtered after 4 h, washed with methanol and water and
dried at room temperature.
–1
The IR spectra were recorded in the range of 4000–150 cm on a Perkin Elmer Sys-
tem 2000 FT-IR spectrometer in the mid–IR range using KBr pellets and polyethylene
pellets in the far–IR range at room temperature. The spectra were obtained with a resolu-
–1
tion of 4 cm and with a co-addition of 16 scans.
The thermal analysis was carried out using a DuPont 2000 TA system with a
thermobalance DuPont 951 TGA. At the thermogravimetric measurements the sam-
–
1
ples (ca. 5 mg) were heated in a platinum crucible with a heating rate of 10 K min up
to 1000 K in flowing air and argon atmospheres. With the same heating rate the DSC
curves were registered up to 600 K using an open aluminium pan as sample holder
and an empty aluminium pan as reference. For the TG-MS measurements a TA In-
struments SDT 2960 was employed, coupled with Balzers Termostar GSD 300 T cap-
illary MS. The measurements were conducted in flowing helium and air atmospheres.
The magnetic moment of the complexes was measured using a magnetic suscep-
tibility balance MSB-MKI, Sherwood Scientific Ltd, Cambridge. The data were cor-
rected for diamagnetic susceptibilities.
Results and discussion
The crystal and molecular structure of the ligand [21] and the Co(L) complex were de-
3
termined by single crystal X-ray analysis [22]. The FT-IR spectra of the cobalt(III)
compounds obtained in the reaction of Co(OAc) and CoSO with HL were identical.
2
4
The structure of the nickel(II) complex was solved on the basis of powder diffraction
X-ray data earlier [22]. The structure of the ligand, I, the copper(II), II, cobalt(III), III
and nickel(II), IV, complexes is presented in Scheme 1.
The elemental analysis data for the copper(II) compound (CuC H N S ,
7 8 4 2
M =276.85) are C: 28.04 (calcd. 30.37), H: 2.92 (calcd. 3.28), N: 18.56 (calcd. 20.24),
r
Cu: 22.07 (calcd. 23.16)%.
All the compounds are colored and stable in air. The copper(II) complex is prac-
tically insoluble in the common solvents; compounds III and IV are soluble in DMS
and DMF, less soluble in acetone, methanol and ethanol and insoluble in water. The
low molar conductivity of the nickel(II) and cobalt(III) compound shows to their
non-electrolytic character.
The lack of the magnetic moment of the cobalt compound points to the oxidation of
the central atom during the complex formation in air, i.e. to the formation of a cobalt(III)
complex. The nickel(II) compound is diamagnetic, referring to a tetra coordinated central
atom which is in accordance with the determined trans-squere-planar structure of the
complex. The magnetic moment of the copper(II) complex (µeff=1.53 µ ) i.e. is some-
B
what less than the expected spin only value for the S=0.5 systems. This suggests a
J. Therm. Anal. Cal., 74, 2003

9
46
MÉSZÁROS SZÉCSÉNYI et al.: TRANSITION METAL COMPLEXES
Scheme 1
dimeric (polymeric) structure for this compound. The dimeric structure is supported also
by the low solubility of the compound [23].
The most probable structure of the copper(II) compound is assumed on the basis
of its IR spectrum [26], compared with the spectrum of the ligand [27].
–1
The strong bands in the spectrum of the ligand in the 3400–3100 cm range are
–
1
characteristic for the primary amide ν(NH ) vibrations (3398 cm NH stretch, 3241
2
2
–1
and 3135 cm asymmetric and symmetric stretch, respectively). In the spectrum of the
complex the intensity of the ν(NH) vibration is lower and its position has changed
–
1
to 3338 cm referring to the deprotonation of the NH -group. The scissoring NH bands
2
2
–1
in the spectrum of the ligand appear at 1600 and 1576 cm together with pyrazole skele-
ton stretch vibrations. In the spectrum of the complex the strong band at 1600 cm has
almost completely vanished, supporting the proposition on the deprotonation of the am-
ide-group. The β(NH) band is shifted to 1572 cm . Bands at 808 and 802 cm in the
spectrum of the ligand and the copper(II) complex, respectively, can be assigned to the
ν(CS) vibration. The intensity of the bands is about the same, suggesting that the sulphur
atom does not take part in the coordination after the deprotonation.
–1
–1
–1
The most significant difference in the FT-IR spectrum of the ligand and in the
spectra of the cobalt(III) and nickel(II)-complexes compared with the spectrum of the
–
1
copper(II) complex is the appearance of a strong band at 2116 cm in the spectrum of
the latter which can be assigned to the ν(SCN) vibration.
Structure II (Scheme 1) can be proposed as most probable for the copper(II)
complex. The relatively large deviation between the calculated and experimentally
determined results of the elemental analysis data may be a consequence of the impu-
J. Therm. Anal. Cal., 74, 2003

MÉSZÁROS SZÉCSÉNYI et al.: TRANSITION METAL COMPLEXES
947
rity of the compound due to a very rapid precipitation process. The very low solubil-
ity of the complex made its purification by recrystallization impossible.
It is interesting to emphasize that in reaction of copper(II) chloride and bromide
with the same ligand, the ligand is coordinated to copper(II) in its neutrale thio-keto
form (unpublished data). The same coordination mode was found in copper(II) halide
complexes with analogous 3,5-dimethyl-1-N-methyl and 1-N-ethyl thiocarboxamide-
pyrazole ligand [19, 20]. This points to the important role of the anions in complex for-
mation reactions.
The influence of the anions on the course of the reaction was investigated using
different nickel(II) salts. Beside NiSO , the reaction was carried out under similar ex-
4
perimental conditions with salts containing anions of different Brønsted basicity:
Ni(CH COO) , Ni(CF COO) and Ni(SCN) . With NiSO and Ni(CH COO) a spon-
3
2
3
2
2
4
3
2
taneous reaction was observed. In the case of the other two salts the complex forma-
tion failed. However, addition of NaOH to the reaction mixture induced the precipita-
tion with Ni(CF COO) and Ni(SCN) also. The infrared spectra of the formed com-
3
2
2
pounds were in all the cases identical referring to formation of identical complexes.
The difference in complex formation in the case of Ni(CH COO) , Ni(SCN)
2
3
2
and Ni(CF COO) may be explained by the decreasing Brønsted basicity of the an-
3
2
ions. The basicity of the acetate ion is high enough for the deprotonation of the ligand
taking into account the crystal field stabilization energy (CFSE), released during
–
–
complex formation. In the case of the SCN and CF COO ions the deprotonation is
3
promoted by adding of NaOH to the solution. The spontaneous reaction in the case of
NiSO cannot be explained on the basis of the Brønsted basicity of the sulfate ion. It
4
is too low as compared to the basicity of the other three ions, while the CFSE remains
the same. As a consequence, some other interactions should be considered, taking
into account Pearson’s soft-hard classification of the acids and bases [28–30]. Ac-
cording to the classification of the ions as soft or hard acids and bases, nickel(II) ion
–
–
–
is a medium soft acid while CH COO , SCN and CF COO ions belong to medium
3
3
soft bases. This assumes a stronger interaction between the ions; the interaction be-
tween the nickel(II) and the hard sulfate base is less explicit, promoting thus the reac-
tion of Ni(II) with the ligand. The solvation energy of the ions in the same solvent are
also different and probably cannot be ignored, either.
Thermal decomposition of the compounds
The thermogravimetrical and DSC curves of the ligand and the complexes were
registred in air and argon atmospheres. The TG-DTG curves of the ligand in air and
argon are presented in Fig. 1, while those of the complexes in air in Fig. 2. The DSC
curves are depicted in Fig. 3.
As is usual, the thermal stability of the ligand is lower than that of the complexes
(
Figs 1 and 2). The endothermic decomposition of the ligand, accompanied by the
melting (Fig. 3) begins at 360 K. In air, at 500 K the decomposition is completed
when the measurement is carried out in an unused aluminum pan. When the decom-
position is measured in a platinum crucible with traces of metal salts, the thermal sta-
J. Therm. Anal. Cal., 74, 2003

9
48
MÉSZÁROS SZÉCSÉNYI et al.: TRANSITION METAL COMPLEXES
Fig. 1 TG and DTG curves of the ligand in air and argon atmosphere
Fig. 2 TG and DTG curves of the complexes in air
J. Therm. Anal. Cal., 74, 2003

MÉSZÁROS SZÉCSÉNYI et al.: TRANSITION METAL COMPLEXES
949
bility of the ligand seems to be higher and above 800 K uncontrolled oxidation pro-
cesses are taking place as was observed with some other thiocompounds [31]. The
ligand decomposition in argon is also complete, but it is finished above 1000 K.
The thermal decomposition of the complexes starts at somewhat higher temper-
ature. The highest thermal stability belongs to the cobalt(III) complex (Fig. 2, 440 K),
while the thermal stability of the nickel(II) and copper(II) complexes is about the
same (≈380 K). The decomposition of the complexes is endothermic. The sharp exo-
thermic peak in the DSC curve of the nickel(II) complex is probably a consequence of
a structural rearrangement.
The thermal decomposition of the nickel(II) compound was followed also by a cou-
pled TG-MS measurement in a helium purge gas. The first decomposition step belongs to
the fragmentation of the ligand, probably to demethylation of the pyrazole ring. By re-
combination of the methyl groups ethane molecules (m/z=30) or C H -fragments are
2 7
forming. In Fig. 4 the m/z=31 amu is shown which probably belongs to the C H -frag-
2
7
ment. Both of the peaks were also detected in the mass spectrum of the 3,5-di-
methylpyrazole but with much less intensity [32]. At higher temperature the highest peak
intensity in the mass spectrum is that with an m/z=28 which may be ascribed to a nitrogen
evolution from the pyrazole ring. In air, the first peak belongs to m/z=44, i.e. the domi-
nant process in the decomposition is an oxidation, resulting in CO
2
formation, but even in
air peaks with m/z=30 and m/z=31 are detectable. Similar decomposition pattern was ob-
3
1
3
served at the thermal decomposition of the Cu(L ) and [CuBr(HL )(L )] complexes
(
2
2
1
3
HL =3,5-dimethylpyrazole, L =3,5-dimethyl-1-carboxamidepyrazolide ion) [33].
At 550 K an intermediate formation is detected which is stable in the 550–650 K temper-
Fig. 3 DSC curves for the ligand and the complexes
J. Therm. Anal. Cal., 74, 2003

9
50
MÉSZÁROS SZÉCSÉNYI et al.: TRANSITION METAL COMPLEXES
Fig. 4 TG–MS coupled curves for Ni(L)
2
ature range. The probable composition of the intermediate is Ni(SCN) (∆m=46.9%,
2
calcd.: 47.64 %). The FT-IR spectrum of the intermediate supports this proposition.
–1
Bands at 2167 and 2113 cm can be assigned to ν(SCN) and ν(NCS) vibrations, thus the
most probable composition of the intermediate is Ni(SCN)(NSC), i.e., the structure con-
tains both thiocyanate and isothiocyanate ligands.
The decomposition of the other complexes is continuous. In the air above 650 K
uncontrolled oxidation processes are taking place (probably because of the metal ion
traces in the platinum crucible). In argon such phenomenon was not observed, but the
decomposition of the complexes is not finished up to 1000 K.
Conclusions
The complex formation of hydrates of copper(II), nickel(II) and cobalt(II) sulfates
with 3,5-dimethyl-1-thiocarboxamidepyrazole is accompanied by the deprotonation
of the ligand. In the reaction in air a cobalt(III) complex, Co(L) is obtained. The
3
structure of the nickel(II) complex, Ni(L) , is trans-square planar [24], while in the
2
case of copper(II) complex the reaction is accompanied also by the structural rear-
rangement of the ligand and a dimeric compound is formed with a probable composi-
tion of [Cu(SCN)L]2.
The role of the anion in the reaction has been studied with various nickel(II)
salts. The complex formation can be related to the basicity of the anions as well as to
the interactions between the nickel(II) ion and the anions. The explanation of the in-
J. Therm. Anal. Cal., 74, 2003

MÉSZÁROS SZÉCSÉNYI et al.: TRANSITION METAL COMPLEXES
951
teractions may be based on Pearson’s theory. The solvation effect probably cannot be
ignored, either.
The thermal stability of the compounds is low. The decomposition is endother-
mic in all the cases. The sharp exotherm peak in the case of the nickel(II) complex
probably belongs to a structural rearrangement during the thermal treatment. The de-
composition of the compounds is continuous except in the case of Ni(L) , where in
2
the temperature range of 550–650 K an intermediate formation is observed. The com-
position of the intermediate on the basis of its FT-IR spectrum is Ni(SCN)(NCS). In
argon the decomposition of the ligand is completed above 1000 K, while the decom-
position of the complexes is not complete in this temperature range. In air
above 650 K uncontrolled oxidation processes are taking place, probably catalysed
by traces of metal salts in the platinum crucible.
*
* *
One of the authors (Katalin Mészáros Szécsényi) would like to thank the Domus Hungarica
Scientiarum Artiumque Foundation for their support. The work was financed in part by the Ministry
for Science and Technologies and Development of the Republic of Serbia.
References
1
2
F. Arcamone, S. Penco, P. G. Orezzi, V. Nicolella and A. Pirelli, Nature, 203 (1964) 1064.
F. Arcamone, P. G. Orezzi, W. Barbieri, V. Nicolella and S. Penco, Gazz. Chim. Ital.,
9
7 (1967) 1097.
3
Lu Ding, L. Grehn, E. De Clercq, G. Andrei, R. Snoeck, J. Balzarini, B. Fransson and
U. Ragnarsson, Acta Chim. Scand., 48 (1994) 498.
4
5
6
7
S. Trofimenko, Chem. Rev., 72 (1972) 479.
S. Trofimenko, Prog. Inorg. Chem., S. J. Lippard (Ed.), Wiley, New York, 34 (1986) 115.
S. Trofimenko, Chem. Rev., 93 (1993) 943.
J. Goslar, P. B. Sczaniecki, M. M. Strawiak and J. Mrozinski, Trans. Met. Chem., 13 (1988)
8
1.
8
9
M. Badea, A. Emandi, D. Marinescu, E. Crstureanm R. Olar, A. Braileanu, P. Budrugeac and
E. Segal, J. Therm. Anal. Cal., 72 (2003) 525.
W. G. Haanstra, Ph.D. Thesis, Leiden University, 2300 RA Leiden, The Netherlands 1991.
1
1
0 R. Mukherjee, Coord. Chem. Rev., 203 (2000) 151.
1 A. Hergold-Brundiº, B. Kaitner, B. Kamenar, V. M. Leovac, E. Z. Ivegeš and N. Juraniº,
Inorg. Chim. Acta, 188 (1991) 151.
12 J. Pons, X. López, E. Benet, J. Casabó, F. Teixidor and F. J. Sánchez, Polyhedron, 9 (1990) 2839.
13 W. Mori, T. Sakurai, A Nakahara and Y. Nakao, Inorg. Chim. Acta, 88 (1984).
14 P. Iliopoulos, G. D. Fallon and K. S. Murray, J. Chem. Soc., Dalton Trans., (1988) 1823.
15 M. Angaroni, G. A. Ardizzoia, T. Beringhelli, G. Monica, D. Gattteschi, N. Masciocchi and
M. Moret, J. Chem. Soc., Dalton Trans., (1990) 3305.
1
1
6 K. Mészáros Szécsényi, E. Z. Ivegeš, V. M. Leovac, Lj. S. Vojinoviº, A. Kovács, G. Pokol,
J. Madarász and ¦. K. Jaºimoviº, Thermochim. Acta, 316 (1998) 79.
7 K. Mészáros Szécsényi, E. Z. Ivegeš, V. M. Leovac, A. Kovács, G. Pokol and
¦. K. Jaºimoviº, J. Therm. Anal. Cal., 56 (1999) 493.
J. Therm. Anal. Cal., 74, 2003

9
52
MÉSZÁROS SZÉCSÉNYI et al.: TRANSITION METAL COMPLEXES
18 K. Mészáros Szécsényi, V. M. Leovac, ¦. K. Jaºimoviº, V. I. ‡ešljeviº, A. Kovács and
G. Pokol, J. Therm. Anal. Cal., 63 (2001) 723.
1
2
2
9 A. K. Barik, P. Bandyopadhyay and S. K. Kar, Polyhedron, 17 (1998) 1.
0 A. K. Barik, S. Paul, R. J. Butcher and S. K. Kar, Polyhedron, 19 (2000) 2651.
1 ¦. K. Jaºimoviº, G. Giester, Z. D. Tomiº and V. M. Leovac, 3 International Conference of the
th
Chemical Societies of the South–Eastern European Countries, 2002, PO 025.
2
2
2 ¦. K. Jaºimoviº, G. Giester, Z. D. Tomiº and V. M. Leovac, Acta Cryst., A58 (2002) C131.
3 M. Krunks, J. Madarász, T. Leskelä, A. Mere, L. Niinistö and G. Pokol, J. Therm. Anal. Cal.,
7
2 (2003) 497.
2
2
2
4 I. R. Evans, J. A. K. Howard, K. Mészáros Szécsényi, V. M. Leovac, ¦. K. Jaºimoviº, J.
Coord. Chemistry (submitted)
5 A. B. Neinding, Magnetochemistry of Trnasition metal Complexes, Results in Sciences (Series
Chemistry), Moscow 1970 p. 205 (in Russian)
6 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Co-ordination Compounds. Part B.
Applications in Co-ordination, Organometallic and Bioinorganic Chemistry, Wiley, New York
th
5
Ed., 1997.
2
7 G. Socrates, Infrared Characteristic Group Frequencies. Tables and Charts. Wiley, New York
nd
2
Ed., 1994.
2
2
3
3
8 R. G. Pearson, J. Am. Chem. Soc., 85 (1963) 3533.
9 R. G. Pearson, Science, 151 (1966) 172.
0 R. G. Pearson and J. Songstad, J. Am. Chem. Soc., 89 (1967) 1827.
1 Atlas of thermoanalytical curves, G. Liptay (Ed.), Vol. 3, No. 160, Akadémiai Kiadó,
Budapest and Heyden and Sons, London 1974.
3
3
2 http://webbook.nist.gov/chemistry, Database 69 – July 2001.
3 K. Mészáros Szécsényi, V. M. Leovac, V. I. ‡ešljeviº, A. Kovács, G. Pokol, Gy. Argay,
A. Kálmán, G. A. Bogdanoviº, ¦. K. Jaºimoviº and A. Spasojeviº-de Biré, Inorg. Chim. Acta,
323C (2003) 253.
J. Therm. Anal. Cal., 74, 2003