Crystallographic, spectroscopic and theoretical investigations on Ni(II) complexes of a tridentate NNS donor thiosemicarbazone

Abstract

Five new nickel(II) complexes [Ni(L)NCS] (1b), [Ni(L)N3] (2), [Ni(L)N(CN)2] (3), [Ni(L)OAc] (4) and [Ni(HL)SO4] (5) of a thiosemicarbazone HL (where HL = 2-benzoylpyridine-N(4)-phenylthiosemicarbazone) including pseudohalides like thiocyanate, azide and dicyanamide have been synthesized and characterized by elemental analysis, magnetic susceptibility, FT-IR, electronic and NMR spectroscopic techniques. The interesting amido-iminol tautomerism enables the pro-ligand to exist in amido form as well as deprotonated iminol form thereby functioning as tridentate NNS donor, coordinating through pyridyl nitrogen atom, azomethine nitrogen atom and amido/iminolate sulfur atom in the complexes. The crystal structures were established by single crystal XRD analysis. Two different single crystals of the compound thiocyanato complex were obtained with and without DMF solvent molecule having triclinic and monoclinic lattices with P1- and P21/n space groups respectively. Also, the compound 2 is having a monoclinic lattice with P21/n space group. Nickel(II) exists in distorted square planar geometry in all the complexes. Further DFT calculations were carried out at B3LYP/TZVP level of theory to obtain an insight on the stability and the nature of frontier orbitals. Finally, electrostatic potential plots mapped on optimized geometries substantiate the noncovalent interactions found in their respective crystal structures.