Benzoic Acid-Based Azo Compound and Its Hg(II) Complex: A Multidimensional Investigation Including Synthesis, Characterization, Quantum Chemical Calculations, and Solvent Extraction Studies

This study presents the synthesis and comprehensive characterization of a novel benzoic acid-based azo ligand, 2-((5-hexyl-2,4-dihydroxyphenyl)diazenyl)benzoic acid (H2PB), and its Hg(II) complex, [HgPB(H2O)]. The structures were elucidated using H-1- and (1)3C-NMR, HRESI-MS, TG-DTA, FT-IR, XRD, UV-vis, magnetic susceptibility, and molar conductance measurements. H2PB behaved as a tridentate ligand, forming a 1:1 metal-to-ligand complex. To gain deeper insights into their molecular and electronic properties, quantum chemical calculations were performed using density functional theory (DFT) with the B3LYP functional with 6-311G(d,p) (for all atoms except Hg) and LANL2DZ (for Hg) basis sets. These calculations included geometry optimization, vibrational analysis, electronic transition projections, NMR chemical shift predictions, HOMO-LUMO analysis, molecular electrostatic potential (MEP) diagram, non-covalent interaction (NCI) analysis, potential energy surface (PES) scanning, and thermodynamic parameter determination. The theoretical spectral data of the H2PB and [HgPB(H2O)] were in good agreement with the experimental ones. Additionally, the ability of H2PB to extract metal ions [Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pb(II), Cd(II), Fe(II), and Hg(II)] from aqueous solution was studied using a solvent extraction method. H2PB exhibited high selectivity for Hg(II), with an extraction efficiency of 89.7%. UV-vis titration experiments also indicated its potential as a chemosensor for Hg(II), suggesting its applicability in environmental mercury remediation.