Bioinspired Co(II) and Zn(II) complexes with an imidazole derived tripodal ligand. Structural models for astacins and MnSOD

Abstract

The syntheses of a new imidazole based tripodal ligand, namely N,N-bis(2-ethyl-4-methyl-imidazo-5-yl-methylen)-glycine (HemiGly) and its complexes with Co(II) and Zn(II) are described. HemiGly was prepared by a modification of the Mannich reaction giving a tripodal tetradentate ligand with a N3O donor set that may model the coordinative environment of some metal ions in biological systems, such as astacin-type enzymes or metal-specific SODs. This article presents the syntheses and characterization of metal complexes with general formula [M(emiGly)X]n+, where n=0, 1 depending on X, which may be either an oxygen donor (from a water molecule or an adjacent carboxylate in the solid state) or an halide or pseudohalide. Cobalt and zinc systems resulted to be isostructural and the geometries of the complexes are driven by the nature of the X ligand: trigonal bipyramidal when X is an halide or pseudohalide and octahedral when X is an oxygen donor. Solution studies also indicate parallel behavior and speciation for Zn(II) and Co(II) complexes. Structural comparison of the pentacoordinated zinc complexes shows a considerable resemblance with the metal site in astacins.