Three new complexes [H 2 en][Ni(pchc) 2 ] (1) (pchc=pyridine-4-carbonyl-hydrazine carbodithioate), [Ni(Hppith) 2 ] (2) (H 2 ppith=1-phenyl-3-pyridin-2-yl-isothiourea) and [Ni(mppcdt) 2 ] (3) {mppcdt=4-(2-methoxyphenyl)piperazine-1-carbodithioate} have been synthesized and characterized by elemental analyses, IR and single crystal X-ray diffraction data. The ligand H 2 ppith and complexes [H 2 en][Ni(pchc) 2 ] (1) [Ni(Hppith) 2 ] (2) and [Ni(mppcdt) 2 ] (3) crystallize in monoclinic, orthorhombic, monoclinic and triclinic system with space group P21/n, Icab, C2/c and P1¯, respectively. The nitrogen and sulfur donor sites of the bidentate ligands chelate Ni(II) forming two five-membered CSN 2 M chelate rings in the complex 1, two six membered C 2 SN 2 M rings in complex 2 and the sulfur donor sites of the bidentate ligand chelate Ni(II) forming two four membered CS 2 M rings in complex 3. The Ni(II) complexes are diamagnetic and have distorted square planar geometry. The crystal structure of the complexes are stabilized by various types of inter and intramolecular extended hydrogen bonding providing supramolecular framework. Results obtained from quantum chemical calculations at the density functional theory level corroborate our experimental findings from IR and UV. The course of the thermal degradation of complexes 1, 2 and 3 has been investigated by TG-DTA. Thermogravimetric analyses of the complexes indicate NIO/NIS as the end residue.