THERMAL LATENT COORDINATION-COMPOUNDS .2. THE THERMAL-DEGRADATION OF IMIDAZOLE AND PYRAZOLE ADDUCTS OF METAL(II) PICOLINATE AND QUINALDINATE

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.) sho w a similar thermal behaviour. Tn the first step of decomposition the corresponding azolinium picolinates or quinaldinates (H(2)AzPa, H(2)Az Qa) 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 ill ustrates a proton transfer and a subsequent thermal removal of benzimi dazolinium quinaldinate (H(2)BzImQa): Hydrogen bridges from pyrrole ni trogen of the benzimidazole to the non-coordinated oxygen of the quina ldinate predetermine the thermal initiated proton transfer. The high v olatility 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 wit h formation of the solvent-free inner complex M(Pa)(2) XIIa-b. From co mpounds XVIIIa-b quinaldic acid or their decomposition products are sp lit off and a high temperature modification of M(Im)(2) XVIIIa-b is fo rmed at elevated temperature. XVIIIa-b are decomposed to the cyanides M(CN)(2) similarly to the thermal behaviour of Cu(Im). In the first st ep 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 coordi nation of the azole heterocycles in copper chelate compounds.