Crystal structure and properties of a new five-coordinate manganese superoxide dismutase mimic

A new five-coordinate manganese(II) complex Mn(NTB)(C8H4O4)·DMF·0.5CH3OH·0.5H2O, where NTB is tris(2-benzimidazolyl-methyl) amine and C8H4O42− is the dianion of terephthalic acid, was prepared and characterized by X-ray crystallography. It crystallizes in the tetragonal system, space group l41/a with a = 28.063(1), c = 22.8680(1) Å, Z = 16 and V = 18009(9) Å3. The structure was solved by direct methods and refined by full-matrix least-squares(on F) to residual R(wR) values of 0.0785 (0.076). The manganese in the complex adopts a distorted trigonal-bipyramidal coordination geometry with an N4O ligand donor set and bears structural similarities to the active site of Mn-superoxide dismutase. The X-band electron paramagnetic resonance spectrum of the complex exhibits a six-line manganese hyperfine pattern with g = 2.005, A = 94 G. The electrochemical properties of the complex were studied in DMF by cyclic voltammetry. The complex can catalyse the dismutation of superoxide (O2−) effectively in the riboflavin-methionine-nitro blue tetrazolium assay.