M. Olczak-Kobza / Thermochimica Acta 419 (2004) 67–71
71
The decomposition of Zn(Han)2(1,2-Meim)2 complex
proceeds in three stages with mass loss of 7.2, 62.3 and
of imidazole does not. Compounds with imidazole and
1,2-dimethylimidazole have a crystalline structure, while
9
4.9%, respectively. The investigation of the gaseous prod-
compound with 4-methylimidazole is amorphous.
−
ucts of the first stage shows partial decomposition of lig-
The o-aminobenzoate ion (NH2C H4COO ) is tridentate
6
ands. The fragment ions of the destruction of benzene (m/z
in homoligand complex Zn(Han)2, however, it is monoden-
tate in heteroligand one. In these complexes, zinc forms
bond with monodentate COO group of o-aminobenzoate
5
0, 51, 52,) are found in the mass spectrum. A specified
−
formula has not been found for the product of this stage.
The total mass loss of the second stage is described by
several overlapping processes (Fig. 3, DTG curve) and the
endothermic peak. The mass loss and the analyses of sinter
ion and with nitrogen N(3) of imidazoles.
Thermal decomposition pathways of the investigated
compounds were determined. The metal–ligand bonds are
cleaved, at first, when pyrolysis of Zn(Han)2(Him)x (x = 3,
5) starts to proceed. The Zn(im)2 compound is the in-
termediate product. The bonds of ligands are cleaved at
the beginning of pyrolysis of Zn(Han)2(4-MeHim)2 and
Zn(Han)2(1,2-diMeim)2. The Zn(an) is the intermediate
product of decomposition.
The pyrolysis progresses through two stages in the case
of the complexes with imidazole and 4-methylimidazole,
and through three stages in the case of the complex of
1,2-dimethylimidazole. Thermal stability, described by Ti,
is the lowest for Zn(Han)2(4-MeHim)2 (Ti = 353 K) and it
is the highest for Zn(Han)2(1,2-diMeim)2 (Ti = 448 K) (Ti:
the temperature at which the rate of the pyrolysis is visible,
kinetic characteristic of pyrolysis [22,23]).
(593 K) show that zinc mono(o-aminobenzoate) is formed.
The third stage is complicated and described by three peaks
in the DTG curve. Zinc is the final product and the big dif-
ference between the theoretical mass loss—87.65% and the
experimental one—94.9% is explained by evaporation of
the metallic zinc. The gaseous products of decomposition
include the following fragment ions: CH3 (m/z 15), NH2
(m/z 16), H2O (m/z 18), NO (m/z 30), CO2 (m/z 44.46),
C H (m/z 78–76, 50–52), C H NH2 (m/z 94.93) and the
6
6
6
5
molecular ion C3N2H4 (m/z 68). The analysis of sinters
and gaseous products indicate the following decomposition
reaction (4):
Zn(Han)2(1, 2-diMeim)2 → ZnXY → Zn(an) → Zn (4)
where ZnXY is not a stechiometric compound.
The thermal decomposition indicates that, in the case of
imidazole complexes, the metal–ligand bonds are cleaved
at first. Zinc imidazolate is the intermediate product
of pyrolysis. The decomposition of the complexes with
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−
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[