Molecular Structure and Nonlinear Optical Response of Magnesium Oxalate: a Theoretical Investigation

Abstract

Magnesium oxalate is an important biomineral and coordination compound with potential relevance in materials science and optoelectronics. In this work, a comprehensive study combining experimental spectroscopic techniques and quantum chemical calculations was performed to elucidate the molecular structure and electronic properties of magnesium oxalate. The optimized geometry obtained at the B3LYP/6-31G(d,p) level confirms the bidentate coordination of oxalate ligands and the mixed ionic–covalent nature of Mg–O bonds. Vibrational assignments from FT-IR and Raman spectra, supported by DFT calculations, revealed characteristic stretching and bending modes of the oxalate framework and Mg–O linkages. Theoretical UV-Vis and NMR spectra further validated the electronic environment and structural symmetry of the complex. Frontier molecular orbital (HOMO–LUMO) analysis highlighted ligand-to-metal charge transfer processes and provided insight into electronic stability and reactivity. Natural bond orbital (NBO) analysis demonstrated strong donor–acceptor interactions, particularly between oxygen lone pairs and antibonding C–O orbitals, accounting for significant charge delocalization within the molecule. The molecular electrostatic potential (ESP) map identified oxygen atoms as preferred electrophilic sites and magnesium as the main electron-accepting center. Global reactivity descriptors, dipole moment, polarizability, and hyperpolarizability values indicate notable nonlinear optical (NLO) behavior, consistent with charge-transfer mechanisms. Overall, this integrated experimental and theoretical approach provides new insights into the bonding, electronic distribution, and optical properties of magnesium oxalate, underlining its potential applications in supramolecular chemistry and optoelectronic devices.