Intramolecularly H-bonded bis-benzimidazole diamide ligand and its Mn(II) complexes: Synthesis, spectral and electrochemical studies

Abstract

New manganese(II) complexes with a diamide ligand N,N'-bis(benzimidazolyl-2yl)(methyl)pentane diamide have been synthesized with the general composition [Mn(GBGA)₂X₂] where X = Cl^-, CH₃COO^-, SCN^-, ClO₄^-. The ligand has been structurally characterized and has been found to adopt a helical structure stabilized by strong intramolecular and intermolecular H-bonding. The ligand crystallizes in the monoclinic space group <i style="">P2_1/c</i>with unit cell dimensions: <i style="">a</i> = 14.180(5) Å, <i style="">b</i> = 8.454(5) Å, <i style="">c</i> = 19.353(5) Å, <img src='/image/spc_char/alpha.gif' border=0>= 90.000°, β=108.232(5)°, <img src='/image/spc_char/gamma2.gif' border=0> = 90.000° and Z=2. X-band solid state EPR spectra for the Mn(II) complexes have been obtained indicating weakly distorted octahedral complexes with <i style="">D</i> ranging between 0.05-0.14 cm^-1. Cyclic votammograms display a quasi-reversible redox wave. The <i style="">E_1/2</i> values follow the order: SCN^- < CH₃COO^-< Cl^- ~ ClO₄^-. Quenching of superoxide anion is studied by cyclic voltammetry. From the plot of total peak current versus concentration of the added Mn(II) catalysts, the break points and turnover of catalyst have been evaluated.