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The relationship between the structures of Cu(II) complexes and their chemical transformations

VIII. Influence of the structures of complexes Cu(NCO)2L2 and Cu(LNCO)2 on the course of their thermal transformations

Journal of Thermal Analysis and Calorimetry
Authors: H. Langfelderová, M. Hvasiijová, J. Kohout, P. Ambrovič, and K. Csomorová

The paper presents the results of a study of the course of thermal decomposition of complexes Cu(NCO)2L2 and Cu(LNCO)2, withL=pyrazole, 3,5-dimethylpyrazole, 3,4,5-trimethylpyrazole and indazole. The DTA curves of Cu(NCO)2L2 show exothermic excursions somewhat below the decomposition temperatures, corresponding to an inner complex nucleophilic addition of a carbon atom (from an NCO group) to the imine nitrogen atom of a pyrazole ligand. In this reaction the carbamoylpyrazolate anion is formed, coordinated to Cu(II). For these reactions the DSC method yielded the followingΔH values: −12.80 kJ mol−1 (L=pyrazole), −8.15 kJ mol−1 (L=3,5-dimethylpyrazole), −19.49 kJ mol−1 (L=3,4,5-trimethylpyrazole) and −11.59 kJ mol−1 (L=indazole). The course of thermal decomposition for Cu(NCO)2L2 after the nucleophilic addition is the same as for Cu(LNCO)2. The structure differences between the distortion isomers of Cu(NCO)2L2 and Cu(LNCO)2 were manifested in the decomposition temperatures and, in some cases, also in the stoichiometry of the decomposition reactions.

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