Seven different dithiophosphonato Ni(II) complexes, [Ni(Xn)(2)], (Xn = (4-MeO-C6H4)PS2(OR) where R = 3pentyl-, X1; R = 1-phenyl-1-propyl-, X2; R = 4-tert-butyl benzyl-, X3; R = diphenylmethyl-, X4; R = 4-tert- butyl cyclohexyl-, X5; R = 3-phenyl-1-propyl-, X6; R = 3-methyl-1-butyl-, X7) and three different dithiophosphinato Ni(II) complexes, [Ni(Yn)(2)], (Yn = (4-MeO-C6H4)PS2(R) where R = 3-methyl-1-butyl-, Y1; R = 2-methyl propyl-, Y2; R = 1-methyl propyl-, Y3) were prepared by the reaction of NiCl2.6H(2)O and the ammonium salts of the corresponding dithiophosphonic and dithiophosphinic acids, [NH4][Xn] and [NH4][Yn], respectively. Starting with these complexes, that were known previously, new organo-dithiophosphonate salts of tris-phenanthroline Ni(II), [Ni(Phen)3][(Xn)2] and organo-dithiophosphinate salts of the same complex, [Ni(Phen)3][(Yn)2], were synthesized and characterized. Structural studies were based on spectroscopic methods (mass spectrometry (ESI), FT-IR, Raman spectroscopy), magnetic susceptibility measurements and elemental analysis. The crystal structures of [Ni(Phen)(3)][(X-1)(2)], [Ni(Phen)(3)][(X-3)(2)], [Ni(Phen)(3)][(X-4)(2)] and [Ni(Phen)(3)][(Y-2)(2)] were determined by single crystal X-ray diffraction analysis. All the complexes were screened against human cell lines for assessing their cytotoxicity. Especially, [Ni(Phen)(3)][(Y-3)(2)] had the highest cytotoxic potency towards the HepG(2) cell line, with an IC50 value comparable to oxaliplatin. Moreover, [Ni(Phen)3][(X1)2]-[Ni(Phen)(3)][(X-3)2(]) were found to have significant cytotoxic activity against the breast cancer cell line with IC50 values of 51.64, 54.19 and 48.58 lM, respectively. (C) 2021 Elsevier Ltd. All rights reserved.