Synthesis, PXRD structure, spectroscopy, cyclic voltammogram, thermal analysis and DFT/TD-DFT calculations of bis[salicylaldehydato-κO,O']nickel(II)

Abstract

The bis[salicylaldehydato-κO,O']nickel(II) (1) was synthesized from reaction of pyridyl-Schiff base ligands, N-2-(R1-pyridyl)salicylaldimine {R1 = H(HL1), 4-CH3 (HL2) and 6-CH3 (HL3)} and nickel(II) acetate via in-situ hydrolysis of the ligands back to the salicylaldehyde (HL'). The molecular structure of 1 was solved by PXRD which disclosed that the two molecules of O^O-chelate ligands formed a O2,O2-coordination sphere around the nickel atom with a square planar geometry. Elemental analysis data show no nitrogen atom in the sample. EI mass spectra exhibit the parent ion peak at m/z = 300. The molar conductance values (Λm = 2.08–2.15 S m2 mol−1) endorse non-electrolyte nature of 1 with metal-to-ligands ratio of 1:2 in DMF. Solid-state magnetic moment value (μeff. = 3.00 μB) suggests paramagnetic nature of the high-spin nickel(II) complex, supported by 1H NMR, UV–vis. (experimental and simulated spectra) and optimized and PXRD structures. DSC analysis recommends an irreversible phase transformation from crystalline-solid to solid–liquid and isotropic-liquid phase. Cyclic voltammograms demonstrate an irreversible one electron charge transfer process for [Ni(L')2]0/[Ni(L')2]− (L' = salicylaldehydato) couple in acetonitrile. Optimized structures and excited state properties by DFT/TD-DFT correspond well to PXRD structure and electronic spectra in solution.