Synthesis, Structural Characterization, and Hirschfeld Surface Analysis of a New Cu(II) Complex and Its Role in Photocatalytic CO 2 Reduction.

A new Cu(II) complex, [CuL 1 L 2 (CH 3 COO) 2 (H 2 O)]·H 2 O, was synthesized by the reaction of Cu(CH 3 COO) 2 ·H 2 O, 6-phenylpyridine-2-carboxylic acid (HL 1 ), and 4-[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]pyridine (L 2 ) in ethanol-water ( v : v = 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 P -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 1 ), one N atom (N2) from 4-[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]pyridine ligand (L 2 ), 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-H … O 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 H … H contacts made the most significant contribution (46.6%) to the Hirschfeld surface, followed by O … H/H … O, N … H/H … N and C … H/H … C contacts with contributions of 14.2%, 13.8%, and 10.2%, respectively. In addition, the photocatalytic CO 2 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.