Thermal behaviour of complexes of antipyrine derivatives II

Article abstract of DOI:10.1007/s10973-005-0462-0

Parent and mixed ligand complexes of cobalt(II) and coppen(II) ions with N,N〉-bis-(4-antipyrylmethyl)piperazine or N,N〉-tetra(4-antipyryl-methyl)-1,2-diaminoethane or/and imidazole as ligand and ClO₄^- or SCN^- as counterion

Full text of DOI:10.1007/s10973-005-0462-0

Journal of Thermal Analysis and Calorimetry, Vol. 78 (2004) 965–972
THERMAL BEHAVIOUR OF COMPLEXES OF
ANTIPYRINE DERIVATIVES II*
I. Labádi1**, Zs. Czibulya1, R. Tudose2 and O. Costisor2,
1Department of Inorganic and Analytical Chemistry, University of Szeged, H-6701- Szeged,
P.O.BOX 440, Hungary
2Timisoara Institute for Chemistry of the Romanian Academy, RO-1900, Timisoara, 24, Bulv.
Mihai Viteazu, Romania
(Received: March 3, 2004; in revised form: June 22, 2004)
Abstract
Parent and mixed ligand complexes of cobalt(II) and copper(II) ions with N,N’-bis-
(4-antipyrylmethyl)piperazine or N,N’-tetra(4-antipyryl-methyl)-1,2-diaminoethane or/and imidazole as
ligand and ClO4 or SCN– as counterion were synthesised and their thermal behaviour was investigated.
-
Keywords: complexes of Co(II) and Cu(II) ions, imidazole, mixed ligand complexes, pyrazolonic
Mannich bases, thermal behaviour
Introduction
Numerous artificial organic compounds are known which alone or in the presence of
different metal ions display therapeutic activity. To elucidate the mechanisms of
therapeutic action of these compounds and their metal complexes, their characterisa-
tion is required. A knowledge of the physical and chemical properties of a compound
and its metal complexes may help to clarify their biological (therapeutic) activity and
allow the prediction of new compounds or complexes with similar or more higher
therapeutic activity.
For study of the correlation between the therapeutic activity and the physical
and chemical properties, antipyrine derivatives were chosen as model compounds,
because they exhibit antipyretic and analgesic activity [2, 3]. Their complexes with
certain metal ions, e.g. Pt(II) and Co(II) ions, exert antitumor activity [4].
Metal complexes of the antipyrine derivatives, N,N’-bis(antipyrylmethyl)-piperazine
(BAMP) and the N,N’-tetrakis(antipyrylmethyl)-1,2-diaminoethane (TAMEN) were studied
earlier [5–10], and their mixed ligand complexes with imidazole (IA) were also prepared and
investigated. As previously [5–10], in the present work the thermal studies were chosen to
*
For part of I of study, see [1]
**
Author for correspondence: E-mail: dome@chem.hu-szeged.hu
1388–6150/2004/ $ 20.00
Akadémiai Kiadó, Budapest
© 2004 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

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obtain information on the stabilities of the investigated complexes. This method is often used
to characterise different organic compounds and their metal complexes of potential therapeu-
tic use [11–15].
N,N’-bis(antipyrylmethyl)piperazine (BAMP)
N, N’-tetrakis(antipyrylmethyl)-1,2-diaminoethane (TAMEN)
Experimental
Preparation and characterisation of complexes
The general procedure for the preparation of the complexes was as follows: The lig-
ands and the metal(II) chloride in stoichiometric ratio were dissolved in methanol or
ethanol, and NaClO4 or NH4SCN was added to precipitate the solid complex. The
solid product was washed, then dried by the usual methods and its composition was
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The structure of imidazole (IA)
determined by the usual analytical methods. The procedures for the preparation of the
complexes and for the determination of their compositions are described in detail
in [10]. Complexes with the following composition were prepared:
Cu2(BAMP)(IA)4(ClO4)4·2H2O
Cu2(TAMEN)(IA)4(ClO4)4
Co2(BAMP)(IA)4(SCN)4
(1)
(2)
(3)
(4)
Co2(BAMP)(IA)4(ClO4)4·2H2O
The following BAMP parent complexes, with known properties [1, 8], were also
prepared:
Co(BAMP)(SCN)2
Co2(BAMP)(ClO4)4
(5)
(6)
Thermoanalytical studies
Thermal analyses were performed with a computer-controlled MOM derivatograph.
Measurements were made between room temperature and 1000ºC at a heating rate of
10ºC min–1. Ceramic crucibles and a nitrogen atmosphere were used, with a-Al2O3 as
reference substance.
Results and discussion
Compositions of the complexes
BAMP may act as a bis bidendate ligand, via two pyrazolonic O atoms and two
piperazine N atoms. TAMEN can coordinate to metal ions as a bis bidendate or a bis
tridentate ligand, via the four pyrazolonic O atoms and two ethylenediamine N atoms
(the pyrazolonic O and the piperazine or ethylenediamine N atoms always form a
chelate ring).
ClO–4 can act as a mono-, bi-, tri- or tetradentate ligand, but its mono- and bidentate
binding modes are common and it is only a weak complexing agent. SCN– can act as a
monodentate (via the N or S atom) or bidentate ligand towards metal ions, but the
monodentate mode is the common one. The water molecule can also act as a
monodentate or bidentate ligand and may complete the coordination sphere around a
metal ion. IA can act as a monodentate or bidentate ligand via one or two N atoms.
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As concerns the compositions of the complexes and the general sequence of co-
ordination ability of the ligands, the BAMP or TAMEN, IA and SCN– are candidates
as participants in the first coordination sphere of the metal ions. SCN–, ClO– and H2O
4
are suggested to be present in the second coordination sphere, or in the first coordina-
tion sphere, if there are not enough coordinating donor atoms in the complexes.
Information on coordination sphere and the coordination modes of the different
ligands, water and anions can be obtained from the electronic spectra, the IR spectra
and the magnetic susceptibility data relating to the complexes [10].
The electronic spectra [10] suggested a distorted tetrahedral coordination sphere
for both the copper and the cobalt complexes 1–4. The IR spectra reveal changes in
the characteristic bands of BAMP, TAMEN and IA, indicating that these ligands are
located in the first coordination sphere around the metal(II) ion. The differences be-
tween the complexes of the two large ligands (BAMP and TAMEN) are the presence
of H2O in complexes 1 and 2, and the IR spectra of the ClO– .
4
It is presumed that the H2O, ClO– and SCN– are located in the second coordina-
4
tion sphere of the metal(II) ion, bound by hydrogen-bonds or electrostatic interac-
tion. Probably the larger size and the presence of the 5th and the 6th donor atoms in the
TAMEN ligand (complex 2) or the presence of SCN– in the BAMP complex (com-
plex 3) prevent the binding of H2O. Both the n4 and n2 bands of theClO– are split to a
4
small extent to two (complexes 1 and 4) or to three (complex 2) bands, caused by the
-
presumed hydrogen-bonds via two and one O atoms of the ClO4 , respectively. The
characteristic band of SCN– (n(C=S)) is split (2080 and 2063 cm–1), as a sign of the
different surroundings of the SCN– in the molecule.
In complexes 5 and 6, octahedral and distorted tetrahedral coordination spheres
were suggested [6] around the cobalt(II) ion; the four donor atoms of the BAMP, the
SCN– and the ClO–4 are coordinated.
Thermoanalytical studies
Copper(II) complexes
Mixed ligand complexes of copper(II) perchlorate with BAMP or TAMEN and IA
(complexes 1 and 2):
Complexes 1 and 2 decompose in a similar way. The thermoanalytical curves
for complex 1 and 2 are shown in Figs 1 and 2, and the suggested decomposition
scheme is presented in Fig. 3.
The curves reveal the release of H2O from the solid compound in the interval
50–150ºC. This step is not observed in the course of the decomposition of complex 2.
A sharp change may be observed in the TG and DTG curves, at 275 and 310ºC for
complexes 1 and 2, respectively, which may be attributed to an explosion-like
decomposition.
At higher temperatures the samples decompose in two steps, and the masses
suggest CuCl (376 and 468°C) and Cu2O (600°C) as intermediate and end-product.
Mixed ligand complexes of cobalt(II) perchlorate and thiocyanate with BAMP
and IA (complexes 3 and 4):
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969
Fig. 1 Thermoanalytical curves of complex 1
Fig. 2 Thermoanalytical curves of complex 2
Fig. 3 Decomposition scheme of complexes 1 and 2
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Fig. 4 Thermoanalytical curves of complex 3
There are many similarities and differences between the thermal behaviour of the
ClO–4 and SCN– complexes; the thermoanalytical curves are shown in Figs 4 and 5.
Perchlorate complex
The ClO–4 complex (complex 4) decomposes in five steps between 140 and 800°C. On
the basis of the mass losses, the suggested decomposition scheme is shown in Fig. 6:
H2O, HClO4, IA and BAMP molecules are released from the solid matrices in the first,
second, third and fourth steps of the decomposition. Co(ClO4)2 and Co(IA–)2 are sug-
gested as intermediates products. Finally, the Co(IA–)2 decomposes and CoO is formed.
Fig. 5 Thermoanalytical curves of complex 4
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LABÁDI et al.: COMPLEXES OF ANTIPYRINE DERIVATIVES
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Fig. 6 Decomposition scheme of complexes 3 and 4
Comparison of the decomposition schemes of complexes 4 and 6 [1] indicates
that IA loses 2 protons (dissociation) at lower temperature than for the BAMP mole-
cule [1] and it these results in the neutral form of BAMP in the course of the decom-
position. If the complex does not contain IA (complex 6), the BAMP dissociates
above 300ºC and the decomposition is accompanied by a continuous loss of mass to
yield Co(ClO4)2 as endproduct.
Thiocyanate complex
Complex 3 decomposes in three steps; the suggested decomposition scheme is shown
in Fig. 6.
A comparison of the decomposition schemes of complexes 3 and 5 permits simi-
lar conclusions as for the ClO–4 complexes. The IA dissociates at lower temperature
than for BAMP, and a similar decomposition scheme can be suggested.
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Conclusions
A comparison of complexes 1 and 2 demonstrates that the TAMEN complex has the
higher thermal stability. It decomposes at higher temperature. The presence of the 5th and
6th donor atom in TAMEN may be responsible for the greater stability of complexes 2
and for the absence of H2O molecules. The distorted tetrahedron around the copper(II)
ion involves the amine N, pyrazolonic O and two imidazole N atoms. The free
pyrazolonic O atoms in TAMEN may bind to ClO–4 or to the imidazole molecules by hy-
drogen bonding and this interaction causes an increase in the stability of the complex.
It is not surprising that the complexes containing ClO–4 undergo explosive-like
decomposition. Comparison of the thermal behaviour of complexes 1 and 3 clearly
indicate that the copper ion, even in the Cu(I) state, must be present for this phenome-
non to be observed.
*
* *
This work was performed in the framework of cooperation between the Hungarian Academy of Sci-
ences and Romanian Academy and was supported financially, in part, by the Hungarian Scientific
Research Foundation (OTKA T 029554).
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