Exploring a novel copper(II) semicarbazone–pyranoquinoline complex: synthesis, spectroscopic profiling, and DFT insights

Abstract

A novel Cu(II) complex was synthesized from a reaction of 2-[(6-ethyl-4-hydroxy-2,5-dioxo-5,6-dihydro-2H-pyrano[3,2-c]quinolin-3-yl)methylidene]hydrazinecarboxamide (PQMHC) ligand with copper sulfate in a molar ratio 1:1 (L:M). Cu(II)-PQMHC complex was characterized by elemental analysis, mass spectra, infrared spectra, molar conductance, electron spin resonance spectra, electronic spectra, and thermal analysis. Kinetic parameters for the thermal decomposition steps were evaluated using the Coats–Redfern equations. The results of spectral data revealed that the ligand behaves as an O2N tridentate donor, coordinating through the hydroxyl group, azomethine nitrogen, and keto oxygen, forming a square planar geometry. Based on DFT, the molecular structure was optimized at B3LYP/6-311G(d, P) for the PQMHC ligand and at B3LYP/GENECP for the Cu(II)-PQMHC complex and interrelated with the experimental results. The optimized geometry of the Cu(II)-PQMHC complex is nonplanner as indicated by the dihedral angles. The HOMO–LUMO energy levels, total dipole moment, molecular electrostatic potential (MEP), thermodynamic properties, natural population analysis (NPA), natural bond orbital (NBO) analysis, non-linear optical (NLO) behavior, along with both global and local chemical reactivity descriptors were investigated. The electronic absorption spectra of the PQMHC ligand and its copper complex were investigated through the time-dependent density functional theory (TD-DFT) method at the CAM-B3LYP.