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, 1 H and 13 C NMR spectroscopy. The ligand Hppt (1)-and complexes 2 and 3 crystallize in the triclinic, monoclinic and orthorhombic system, space group P 1¯, 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⋯ N secondary interactions. Crystal structure of complex 2 is also stabilized via weak π⋯ π and C–H⋯ π interactions. The crystal structure of complex 3 is stabilized by intermolecular/intramolecular Hg⋯ S interactions and C–H⋯ π interactions. The ligands Hppt and [K (mpcdt)] exhibit green emissions and complex 2 shows photoluminescence due to the presence of Hg⋯ N interactions, whilst complex 3 does not show photoluminescence because Hg⋯ 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⋯ 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).