Synthesis, structure, spectroscopic properties, DFT and TDDFT investigations of copper(II) complex with 2-(2-hydroxyphenyl)benzimidazole

A Cu(II) complex with 2-(2-hydroxyphenyl)benzimidazole [Cu(pbm)2] (1), (Hpbm = 2-(2-hydroxyphenyl)benzimidazole) has been prepared and isolated under hydrothermal condition, and its structural and spectroscopic properties thoroughly investigated. The square-planar geometry was verified by both the density functional theory level (DFT) calculation and X-ray crystallography. A further theoretical analysis of electronic structure of this complex has also been undertaken to gain a deeper insight into the properties of relevant molecular orbitals. The time-dependent density functional theory level (TDDFT) calculation, together with DFT-based molecular orbital analyses, demonstrates that the low-lying absorption bands in UV–vis spectrum are all mainly π → d x 2 – y 2 and/or ( P, σ ) → d x 2 – y 2 ligand-to-metal charge transfer transition (LMCT) in nature.