Studies on phenylmercury(II) complexes of nitrogen-sulfur ligands: Synthesis, spectral, structural characterization, TD-DFT and photoluminescent properties

The reactions of phenylmercury(II) acetate with N-phenyl-5-(pyridin-4-yl)-1,3,4-thiadiazol-2-amine (Hppt) (1) and potassium N(4-methylpiperazine)-1-carbodithioate [K(mpcdt)] yielded [PhHg(ppt)] (2) and [PhHg(mpcdt)] (3). The complexes have been characterized by elemental analyses, IR, UV-Vis, H-1 and C-13 NMR spectroscopy. The ligand Hppt (1)- and complexes 2 and 3 crystallize in the triclinic, monoclinic and orthorhombic system, space group P (1) over bar, C 2/c and Pbca, respectively. The crystal X-ray studies revealed that complexes 2 and 3 both form a one dimensional metal-organic structure, with a linear N-Hg-Ph and S-Hg-Ph core respectively. The most noteworthy features in complex 2 is that the ligand bound phenylmercury cation is stabilized via intramolecular as well as intermolecular weak Hg center dot center dot center dot N secondary interactions. Crystal structure of complex 2 is also stabilized via weak pi center dot center dot center dot pi and C-H center dot center dot center dot pi it interactions. The crystal structure of complex 3 is stabilized by intermolecular/intramolecular Hg center dot center dot center dot S interactions and C-H center dot center dot center dot pi interactions. The ligands Hppt and [K(mpcdt)] exhibit green emissions and complex 2 shows photoluminescence due to the presence of Hg center dot center dot center dot N interactions, whilst complex 3 does not show photoluminescence because Hg center dot center dot center dot S interactions show quenching behaviour in the solid state. The solution state photoluminescence properties of complex 2 indicate that intermolecular as well as intramolecular Hg center dot center dot center dot N interactions persist even in very dilute solution. The geometrical optimization of Hppt (1), [K(mpcdt)) and complexes 2 and 3 was calculated in the gas phase using density functional theory (DFT) with the B3LYP hybrid functional, and was used to predict their molecular properties. The electronic excitation energies and intensities of the six lowest-energy spin allowed transitions were calculated using time dependent density functional theory (TD-DFT). (C) 2013 Elsevier Ltd. All rights reserved.