Template synthesis of square-planar Ni(II) complexes with new thiophene appended Schiff base ligands: Characterization, X-ray structure and DFT calculation

The square planar nickel(II) complexes have been synthesized by the reaction of nickel(II) chloride hexahydrate and the in situ condensed thiophene appended Schiff base ligands of thiophene-2-ethylamine with 3,5-dimethyl-2-hydroxybenzaldehyde or 3,5-dichloro-2-hydroxybenzaldehyde for [Ni(L1)2] (1) and [Ni(L2)2] (2) respectively. The complexes have been characterized by several spectroscopic techniques, viz. FT-IR, 1H NMR, absorption and emission spectroscopy. The complexes crystallize in monoclinic crystal system with C2/c space group for 1 and triclinic crystal system with P−1 space group for 2. In complex 1 the nickel sits on an inversion centre with symmetry –x, 2–y, –z. Cyclic voltammgrams of the complexes show quasi-reversible NiII/NiIII oxidation couple along with irreversible NiII/NiI reduction. Electronic structure and spectral properties are well interpreted by DFT and TDDFT calculations.