Synthesis, Structural Characterization, and Hirschfeld Surface Analysis of a New Cu(II) Complex and Its Role in Photocatalytic CO Reduction

A new Cu(II) complex, [CuLL(CHCOO)(HO)]·HO, was synthesized by the reaction of Cu(CHCOO)·HO, 6-phenylpyridine-2-carboxylic acid (HL), and 4-[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]pyridine (L) in ethanol-water (: = 1:1) solution. The Cu(II) complex was characterized using elemental analysis, IR, UV-vis, TG-DTA, and single-crystal X-ray analysis. The fluorescence properties of the copper complex were also evaluated. The structural analysis results show that the Cu(II) complex crystallizes in the triclinic system with space group -1. The Cu(II) ion in the complex is five-coordinated with one O atom (O2) and one N atom (N1) from one 6-phenylpyridine-2-carboxylate ligand (L), one N atom (N2) from 4-[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]pyridine ligand (L), one O atom (O4) from acetate, and one O atom (O5) from a coordinated water molecule, and it adopts a distorted trigonal bipyramidal geometry. Cu(II) complex molecules form a two-dimensional layer structure through intramolecular and intermolecular O-HO hydrogen bonding. The two-dimensional layer structures further form a three-dimensional network structure by π-π stacking interactions of aromatic rings. The analysis of the Hirschfeld surface of the Cu(II) complex shows that the HH contacts made the most significant contribution (46.6%) to the Hirschfeld surface, followed by OH/HO, NH/HN and CH/HC contacts with contributions of 14.2%, 13.8%, and 10.2%, respectively. In addition, the photocatalytic CO reduction using Cu(II) complex as a catalyst is investigated under UV-vis light irradiation. The findings reveal that the main product is CO, with a yield of 10.34 μmol/g and a selectivity of 89.4% after three hours.