Mercury(II) complexes with 5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione: Synthesis, structural characterization, and theoretical studies

New Hg(II) complexes with 5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione (L) and various halogen ions were synthesized. Based on elemental analysis and flame atomic absorption spectroscopy, complexes have general formula HgL2X2 (X = Cl− (1), Br− (2), and I− (3)). These compounds have been studied by IR, 1H and 13C NMR spectroscopy at room temperature. According to X-ray diffraction analysis, complex 2 crystallizes in monoclinic system. Hg(II) ion has been surrounded by a distorted tetrahedral arrangement of two monodentate ligands (each one coordinating by a Npyridine ring atom) and two bromine atoms. Based on crystal packing findings, intermolecular classical H-bonds of the type NH⋯O and non-classical H-bonds of the type CH⋯O and CH⋯Br, as an important member of noncovalent interaction family, are driving forces for the formation of a very distorted structure. Theoretical studies showed that neither the size of the halide anion nor the intramolecular interactions between two ligands are the reason for the very small NHgN bond angle, observed in complex 2.