Redox potential tuning by redox-inactive anions in copper(II) complexes of non-innocent o-aminophenol-based ligand containing benzoxazole: Learning from nature

Abstract

Four copper complexes of three-dentate benzoxazole-containing o-aminophenol based ligand (H2LBAP) have been synthesized and characterized by IR spectroscopy, UV–Vis spectroscopy, electronic structure calculations, single crystal X-ray diffraction, magnetic susceptibility studies and cyclic voltammetry techniques indicating that the ligand is oxidized to the o-iminosemiquinone form [LBIS]− in copper complexes, CuLBISX, (X=Br−, I−, N3−, NO3−). LBISCuIINO3 is square pyramidal complex while the three other complexes show a distorted tetrahedral geometry. In all structures the ligand is coordinated to CuII via the benzoxazole, as well as the nitrogen and oxygen atoms from the o-iminosemiquinone moiety. The monodentate bromide, iodide, azide, and bidentate nitrate groups occupy the fourth and/or fifth positions in LBISCuX, respectively. The magnetic susceptibility and EPR studies confirm that all complexes are diamagnetic due to the interaction of d9 CuII center and iminosemiquinone radical ligand. Electrochemical redox and consequently catalytic results of complexes revealed that they have been tuned by X anion coordinated to Cu(II).