A tridentate Schiff base ligand (5-methyl-2-hydroxy-acetophenone-S-methyl-thiosemicarbazone, H2L) and its mononuclear nickel complex, [NiL(PPh3)], were obtained and characterized by spectroscopic techniques. Structural analysis of the compounds was supported by complementing crystallographic studies. The X-ray data related to molecular geometries was used in the DFT/B3LYP calculations with 6-311G (d, p) and LANL2DZ (for nickel atom) basis sets. Atomic charge distribution data indicated that the negative charges of free thiosemicarbazidato ligand were transferred to nickel (II) by the formation of the metal complex. To understand the nucleophilic or electrophilic reaction capabilities the ligand and nickel complex, the molecular electrostatic potential (MEP) and electrostatic potential (ESP) analyses have performed. (C) 2018 Elsevier B.V. All rights reserved.