Dinuclear copper(II) complex with a benzimidazole derivative: Crystal structure, theoretical calculations, and cytotoxic activity

Abstract

This work describes a facile synthesis of 5,6‐dimethyl‐2‐(pyridin‐2‐yl)‐1‐[(pyridin‐2‐yl)methyl]‐1H‐benzimidazole (dppb) and the preparation of a dinuclear copper(II) complex bearing this ligand in a ring‐like conformation of formula [Cu(dppb)(acn)ClO4]2(ClO4)2·4acn (1), where acn represents acetonitrile. The crystal structure of the complex was determined by single‐crystal X‐ray diffraction experiment, which showed that dppb acts as a bridge in 1 due to its bidentate–monodentate μ‐κ2NN′:κN″coordination mode, and the coordination sphere of each metal center is completed by one acn molecule and one perchlorate ion. The structure of dinuclear copper(II) complex is symmetric and the two square–pyramidal copper(II) centers are separated by 5.381(1) Å. The geometry optimization, electronic structure, and vibrational spectrum of the [Cu(dppb)(acn)ClO4]22+ cation were calculated using the density functional theory method. The geometrical parameters obtained theoretically were remarkably similar to those observed in the crystal structure of 1 and the calculated vibrational frequencies are in satisfactory coherence with experimental data. In solution, the prepared complex can bind to DNA (Kb = 1.43 × 105 M−1) and inhibit the growth of a human chronic myelogenous leukemia cell line (K562) in a concentration‐dependent manner; importantly, it is almost four times more active than the corresponding free benzimidazole.