Synthesis, crystal structure, and computational study of a new mononuclear Cu(II) complex: Structural insights into the photocatalytic degradation of methylene blue

A new mononuclear Cu(II) complex, [Cu(piv)₂(2-Me-imi)₂] (where piv = pivalic acid; 2-Me-imi = 2-methyl imidazole) was synthesized and structurally fully characterized. Structural analysis reveals that the complex has two isostructural units and in these units, each Cu(II) atom exhibits the same coordination number and environment. Based on CShM calculations, the structure is characterized by a "seesaw" core (SS-4) that extends into a distorted octahedral geometry (OC-6) via elongated axial Cu-O bonds. Each Cu(II) metal ion has distorted octahedral geometry, formed by two nitrogen atoms coming from 2-methylimidazole and two shorter basal oxygens from pivalate ligands, supplemented by two elongated axial Cu-O bonds. The complex forms a 1D supramolecular architecture consisting of helical chains stabilized by N-H···O hydrogen bonding between pivalate and imidazole moieties. The catalyst demonstrates 75.5% photocatalytic degradation of methylene blue (MB) dye in 50 minutes, following pseudo-first-order kinetics. The degradation of MB dye using complex 1 in the presence of various scavengers was investigated and identify the production of active species which are involved in the degradation process. The complex 1 accompanied recyclability over four cycles with degradation efficiency reaching 70.4% after the 4th catalytic run. The structural integrity of the complex used in DFT calculations is supported by the close agreement between experimental Single-crystal X-ray Diffraction (SXRD) data and theoretical Density Functional Theory (DFT) calculations. Time-dependent density functional theory (TD-DFT) analysis using the PBE1PBE functional reveals a HOMO-LUMO gap of 2.64 eV, supporting an Oxygen-to-Metal Charge Transfer (OMCT) mechanism.