Spectroscopic, EPR, X-ray structural, and DFT studies of the complex compound of N4-donor ligand with copper(II)

Abstract

A new mononuclear neutral five-coordinate copper(II) coordination compound [Cu(L)(H2O)] (1) (L = 6,6′-bis(NH-benzimidazol-2-yl)-2,2′-bipyridine) was synthesized and characterized by IR, UV–Vis, EPR and LC-MS (APCI) analysis. The crystal structure was also determined by X-ray crystallography. In 1, the copper(II) center adopts a five-coordinate distorted square-pyramidal (SP) geometry in which the basal plane formed by four of the nitrogen atoms of the ligand while the apical position is occupied by the oxygen atom of the water molecule. The four Cu–N bond lengths are 1.987(4), 1.992(4), 2.020(5) and 2.027(4) Å, and the longest bond of the apical Cu−Ow is 2.234(4) Å. The ligand undergoes deprotonation upon coordination to the metal center and acts as a dianionic tetradentate chelate to form a neutral complex [CuN4O]. The X-band EPR data of 1 are in agreement with the crystallographic data indicating a typical five-coordinate SP geometry. This geometry is also obtained by Density Functional Theory calculations. Time-dependent (TD) DFT calculations were used to shed light on the assignment and the nature of the electronic transitions observed in the UV–Vis spectrum. The calculated results are found to be consistent with the experimental data. Non-linear optical properties were also calculated by DFT calculations.