Crystal structure, configurational and DFT study of nickel(II) complexes with N2O-donor type Schiff base ligand

Nickel(II) complexes containing a Schiff base (L) derived from 2-pyridinecarboxyldehyde and 2-furoic hydrazide [Ni(HL)(L)]NO3 (1) and [Ni(L)2]4H2O (2) where HL = N'-[(E)-pyridin-2-yl-methylidene]furan-2-carbohydrazide, have been synthesized and comprehensively characterized via physico-chemical techniques as well as by single crystal X-ray structural analysis. In both the complexes, the ligand behaves as mono-anionic tridentate and binds to the nickel(II) ion via deprotonated carbonyl-oxygen, pyridine-nitrogen and azomethine-nitrogen. Magnetic moments and electronic studies suggest an octahedral geometry around nickel(II) ion in both the complexes. The supramolecular architecture in both (1) and (2) are shown by C-H...π and π…π interactions. The molecular structures and spectral properties of the complexes have been explained by DFT and TD-DFT calculations. The electronic excitation energies of these complexes, calculated at TD-DFT levels, are in agreement with values deduced from the experimental UV-visible spectra