Authors:M. Döring, J. Wuckelt, W. Ludwig and H. Görls
Complexes of the type M(Pa)2(HAz)2 and M(QA)2(HAz)2 (M=cobalt(II) and nickel(II); HPa=picolinic acid, HQa=quinaldic acid; HAz=azoles like imidazole (Him), pyrazole (HPz), benzimidazole
(HBzIm) etc.) show a similar thermal behaviour. In the first step of decomposition the corresponding azolinium picolinates
or quinaldinates (H2AzPa, H2AzQa) are split off with formation of polymeric mixed ligand complexes M(Pa)(Az) or M(Qa)(Az). X-ray analysis of Co(Qa)2(HBzIm)2 XIIIa illustrates a proton transfer and a subsequent thermal removal of benzimidazolinium quinaldinate (H2BzImQa): Hydrogen bridges from pyrrole nitrogen of the benzimidazole to the non-coordinated oxygen of the quinaldinate predetermine
the thermal initiated proton transfer. The high volatility of the heterocyclic acids and the nitrogen coordination are responsible
for the formation of the mixed ligand complex Co(Qa)(BzIm) XIVa.
Exceptions are the complexes M(Pa)2(HPz)2 XIa-b and M(Qa)2(HIm)2 XVIIa-b. Pyrazole is eliminated from the complexes XIa-b with formation of the solvent-free inner complex M(Pa)2 XIIa-b. From compounds XVIIIa-b quinaldic acid or their decomposition products are split off and a high temperature modification
of M(Im)2 XVIIIa-b is formed at elevated temperature. XVIIIa-b are decomposed to the cyanides M(CN)2 similarly to the thermal behaviour of Cu(Im).
In the first step the thermal degradation of imidazole and pyrazole adducts of copper(II) picolinates and quinaldinates is
characterized by the elimination of azoles. The reason for this thermal behaviour is the weaker coordination of the azole
heterocycles in copper chelate compounds.