Similarities and differences of thermal behaviour of 2-hydroxymethylbenzimidazole complexes with Zn(II) and Cd(II) ions

For a comparison of structural data and thermal behaviour of Zn(II) and Cd(II) complexes with biologically important ligand, 2-hydroxymethylbenzimidazole (L) the complex of the formula ZnL₃](NO₃)₂L_0.67L′_0.33 was prepared and characterized by elemental analysis, infrared (IR) spectra, single-crystal X-ray diffraction and thermal analysis (where L′ = 2-carbaldehydebenzimidazole). IR and X-ray studies have confirmed a bidentate fashion of coordination of the 2-hydroxymethylbenzimidazole to Zn(II) ion (through the nitrogen atom of heteroaromatic ring and oxygen atom of hydroxymethyl group). The zinc ion is hexacoordinated and the shape of polyhedron can be described as pseudo-octahedron (N₃O₃ chromophore type). The decomposition process of studied Zn(II) and Cd(II) benzimidazole complexes in the air atmosphere proceeds in three or four main stages and traces structures of complexes. On the basis of the first DTG_max of the decompositions the thermal stability of the complexes follows the order: CdL₃](NO₃)₂LEtOH_0.25 < CdL₂(NO₃)₂] < ZnL₃](NO₃)₂L_0.67L′_0.33. As the final solid products of thermal decomposition suitable metal oxides are formed.