Cyano-Bridged 'Oximato' Complexes: Synthesis, Structure, and Catalase-Like Activities

The reaction of the oximato-ligand precursor A (Fig. 1) and metal salts with KCN gave two mononuclear complexes [ML(CN)(H2O)n](ClO4) (1 and 2; L={N-(hydroxy-?O)-a-oxo-N'-[(pyridin-2-yl-?N)methyl[1,1'-biphenyl]-4-ethanimidamidato-?N'}; M=CoII (1), CuII (2); n=2 for CoII, n=0 for CuII; Figs. 2 and 3). The new cyano-bridged pentanuclear oximato complexes [{ML(H2O)n(NC)}4M1(H2O)x](ClO4)2 (36) and trinuclear complexes [{ML(H2O)n(NC)}2M1L](ClO4) (710) ([M1=MnII, CuII; x=2 for MnII, x=0 for CuII] were synthesized from mononuclear complexes and characterized by elemental analyses, magnetic susceptibility, molar conductance, and IR and thermal analysis. The four [ML(CN)(H2O)n]+ moieties are connected by a metal(II) ion in the pentanuclear complexe 36, each one involving four cyano bridging ligands (Fig. 4). The central metal ion displays a square-planar or octahedral geometry, with the cyano bridging ligands forming the equatorial plane. The axial positions are occupied by two aqua ligands in the case of the central Mn-atom. The two [ML(CN)(H2O)n]+ moieties and an oximato ligand are connected by a metal(II) ion in the trinuclear complexes 710, each one involving two cyano bridging ligands (Fig. 5). The central metal ions display a distorted square-pyramidal geometry, with two cyano bridging ligands and the donor atoms of the tridentate oximato ligand. Moreover catalytic activities of the complexes for the disproportionation of hydrogen peroxide (H2O2) were also investigated in the presence of 1H-imidazole. The synthesized homopolynuclear CuII complexes 6 and 10 displayed eficiency in disproportion reactions of H2O2 producing H2O and dioxygen thus showing catalase-like activity.