Five new dithiophosphonic acids ((p-MeO-C6H4)PS(SH)(OR), HLn, (n = 1-5); R = 3-pentyl-, HL1; R = 1-phenyl-1-propyl-, HL2; R = 4-tert-butyl benzyl-, HL3; R = diphenylmethyl-, HL4; R=4-tert-butylcyclohexyl-, HL5) were prepared by the reaction of Lawesson reagent with the corresponding alcohols. As the acids were viscous liquids and difficult to purify they were converted to their ammonium salts ([NH(4)Ln]) for purification through crystallization. Four coordinated Ni(II) complexes of the dithiophosphonates ([Ni(Ln)(2)]) were synthesized in methanol medium and purified. The reaction between these square planar complexes and pyridine was carried out to produce six coordinated pyridine derivatives ([Ni(Ln)(2)(py)(2)]). The structures of the fifteen compounds so prepared were elucidated by spectroscopy, elemental analysis methods and magnetic susceptibility measurement. The molecular and crystal structure of [Ni(L2)(2)(py)(2)] was determined by X-ray crystallography. DFT calculations were carried out using the B3LYP functional with the LANL2DZ basis set to the optimized geometrical structure and determine the energies, the orientations of the molecular orbitals (HOMOs and LUMOs) and the molecular electrostatic potential (MEP) surfaces of the octahedral complex [Ni(L2)(2)(py)(2)]. The results for [Ni(L2)(2)(py)(2)] revealed that these bonded to the active sites of A-DNA and B-DNA by weak non-covalent interactions, which was also supported by molecular docking investigations. (C) 2018 Elsevier B.V. All rights reserved.