One-pot synthesis, crystal structure, Hirshfeld surface analysis and characterization of mercury(II) chloride complexes with N,N-donor Schiff base ligands derived from 2-pyridinecarboxaldehyde

Two new mercury(II) chloride complexes with bidentate N,N-donor Schiff base ligands — (E)-2-((pyridin-2-ylmethylene)amino)butan-1-ol (L1) and (E)-2-((pyridin-2-ylmethylene)amino)ethanol (L2) — have been synthesized via a one-pot reaction and characterized as [HgCl2(L1)]2 (1) and [HgCl2(L2)]n (2). Comprehensive characterization was performed using elemental analysis, molar conductance, FT-IR, UV–visible, 1H NMR, and fluorescence spectroscopy. Crystallizing in the triclinic space group P–1, complex 1 features a binuclear structure with each Hg(II) ion adopting a distorted square pyramidal geometry. Complex 2 crystallizes in the monoclinic space group I2/a as a one-dimensional polymeric chain, with each metal center exhibiting a distorted octahedral geometry. Hirshfeld surface analysis indicates significant noncovalent interactions __especially H···H, Cl···H, O···H, and C···H contacts — that contribute to crystal packing. The low molar conductance values in acetonitrile suggest their non-electrolytic nature. UV–visible and fluorescence studies support intramolecular charge transfer (ICT) transitions and weak metal-to-ligand charge transfer (MLCT) bands, attributed to transitions from Hg(II) to the π* orbitals of the ligands.