Thermal behaviour of biologically interesting coordination compounds obtained by reaction of some divalent metal ions with imidazole and N-methyl imidazole

The imidazole ring appears in a number of biological ligands and many different parameters, such as basicity of the ligands, π-electron acceptor ability, steric factors, hydrogen bonding, etc., play an essential role either on the structural types of coordination or on the thermal characteristics of the coordination compounds obtained by reaction of imidazole and its derivatives with transition metal ions. The influence of some of these parameters on the thermal properties of coordination compounds obtained by reaction of imidazole (Im) and N-methyl imidazole (NmIm) with Co(NO3)2, NO(NO3)2 and Cu(NO3)2 is studied here by means of thermogravimetric and differential scanning calorimetric methods supported by infrared spectroscopy. The compounds obtained were Me(L)n(NO3)2 (Me=Co(II), Ni(II), Cu(II); n = 4, 6). The imidazole complexes are always more stable than the corresponding N-methyl imidazole complexes and the ΔH value corresponding to metal-ligand bond breaking is higher for the imidazole compounds. The decomposition mechanisms are also discussed.