Comparison of the complexing processes of 1-butyl-2-hydroxymethylimidazole and 1-butyl-2-methylimidazole in aqueous solution

The stability constants and structures of the complexes of CoII, NiII, CuII and ZnII with 1-butyl-2-methylimidazole (bmim) and 1-butyl-2-hydroxymethylimidazole (bhmim) in aqueous solution have been determined by potentiometric and spectrophotometric methods. The stability of transition-metal complexes of bhmim depends on the presence of the hydroxymethyl group the oxygen atom of which interacts with the metal ion. Cobalt(II) and ZnII form both tetrahedral and octahedral species with either ligands. In the case of bhmim the additional interaction of the oxygen atom shifts the octahedron ⇌ tetrahedron equilibrium in solution towards six-co-ordination.