The syntheses of the complex nickel salt [NiL2] · 2H2O (I) (HL is 2-[2′-(oxymethyldiphenylphosphinyl) phenyldiazenyl]-4-tert-butylphenol) was described. The basic vibrational frequencies in the IR spectra of I were interpreted. Crystal structure of I was determined by X-ray crystallography: the crystals are triclinic, a = 10.331(2) Å, b = 11.310(2) Å, c = 11.641(2) Å, α = 87.48(3)°, = 89.10(3)°, = 82.06(3)°, V = 1345.8(5) Å3, Z = 1, space group P\documentclass[12pt]{minimal}
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$$\end{document}R = 0.0554 (for 3358 reflections with I > 2σ (I)). The coordination polyhedron of the nickel atom is a centrosymmetric square formed by the oxygen atom of the substituted phenol and one of the nitrogen atoms of the azo group of each of the two deprotonated bidentate chelating ligands L− (Ni-N, 1.887(2) Å; Ni-O, 1.810(2) Å). In the crystal of I, complex molecules are stacked to form a layer parallel to the ab plane. The crystal water molecules are located in a layer stabilize it by hydrogen bonds with the complexes.