COMPLEXES OF BIOLOGICALLY IMPORTANT LIGANDS - THERMAL-PROPERTIES OF COORDINATION-COMPOUNDS OBTAINED BY REACTION OF SOME DIVALENT METAL-IONS WITH 2-METHYLIMIDAZOLE AND 4-METHYLIMIDAZOLE

The role of the imidazole group of the histidyl residue in proteins is very important in the understanding of the reactivity and the mechanisms of interaction between proteins and several metallic ions. The ligand power of the imidazole and its derivatives is correlated with the basicity of the molecule, the π- and σ-electron-acceptor ability, the hydrogen bonding ability and the steric hindrance of the molecules. The thermal characteristics of coordinationcompounds obtained by reaction of CoII, NiII and CuII with 2-methyl- and 4-methylimidazole are studied here by means of thermoanalytical techniques, and IR and reflectance spectroscopy and compared with those of the coordinationcompounds obtained by reaction of the same ions with imidazole and N-methyl-imidazole previously published. The compounds prepared were Me(HL)x(NO3)2, (MeCoII, NiII or CuII; HL2-methylimidazole (2mIm) or 4-methylimidazole (4mIm); x = 4 or 6). Two different forms of Co(2mIm)4(NO3)2 and Ni(2mIm)4(NO3)2 showing different thermal and spectroscopic characteristics were obtained.