A novel metal-organic planar NiS4 - type complex, trans-Ni(II)-bis[O-(2-butoxyethyl)-(4-methoxyphenyl)dithiophosphonate], was synthesized by the reaction of ammonium salt of O-dithiophosphonic acid with Ni(CH3COO)(2). The crystal structure of Ni(II)-complex was determined by X-ray Diffraction (XRD) analysis. As a result of the X-ray crystal and molecule structure analyses of the studied trans-Ni(II)-complex, it was obtained that the central nickel atom is coordinated by four sulphur atoms in slightly distorted a square-planar geometry. The X-ray structure confirms a trans isomer of the Ni(II)complex. The Ni(II)-complex crystallizes in the monoclinic space group C12/c1 with unit cell parameters a 22.376(3) (angstrom), b 18.466(3) (angstrom) and c 8.6875(13) (angstrom). In addition, theoretical calculations with the basis set of B3LYP/6-311 + G(2d,p) are performed to determine the structural properties, FT-IR, NMR spectrum, electronic properties and NBO analysis of the compound. The experimental and computed results of the Ni(II)-complex were found to be in good agreement. (C) 2018 Elsevier B.V. All rights reserved.