Some new complexes of [NiL 1 (PR 3 )] (where L 1 = (E)-1-[(2-Amino-5-nitrophenyl)imino-methyl]naphthalene-2-olate, R = Bu and Ph) containing tridentate ONN Schiff base were synthesized and characterized by FT-IR, UV–Vis, 1 H-NMR spectroscopy and elemental analysis. The geometry of [NiL 1 (PBu 3 )] complex were determined by X-ray crystallography. It was indicated that the complex have a square planar structure and four coordinates in the solid state. Theoretical calculations were also performed for [NiL 1 (PBu 3 )] and [NiL 2 (PBu 3 )] L 2 = (E)-1-[(2-hydroxiphenyl)imino-methyl]naphthalene-2-olate to optimize the structures of the ligands and complexes in the gas phase and ethanol solvent, separately to confirm the structures proposed by X-ray crystallography. In addition, UV-Visible and FT-IR spectra of the complexes were calculated and compared with the corresponding experimental spectra to complete the experimental structural identification. The synthesized complexes were incorporated into the TiO 2 nanoparticles. The mixed complexes and TiO 2 nanoparticles were calcinated at 650°C. All nanoparticles were identified via FT-IR, FE-SEM, TEM and XRD.