Nickel(II) complexes having different configurations controlled by N,N,O-donor Schiff-base ligands in presence of isothiocyanate as co-ligand: Synthesis, structures, comparative biological activity and DFT study

Four mononuclear nickel(II) complexes, viz. [NiL1(OAc)(H2O)2]·2H2O (1), [NiL1(NCS)(H2O)2]·H2O (1a), [NiL2(OAc)(H2O)] (2), and [NiL2(NCS)] (2a) (where HL1 = 2-[(2-Morpholin-4-yl-ethylimino)-methyl]-phenol and HL2 = 2-[(2-Pyrrolidin-1-yl-ethylimino)-methyl]-phenol) have been synthesized and structurally characterized. Single crystal X-ray analysis reveals the presence of square planar coordination geometry about nickel for 2a, whereas others have distorted octahedral geometry. DFT calculations have done to explore the origin of different geometries of 1a and 2a although their preparative procedure is same. The influence of different geometries i.e., octahedral and square-planar on the anticancer activity of Ni(II) have been investigated on Erhlich’s ascities carcinoma (EAC) cells and the order of anticancer activity is 2a > 1a > 2 > 1. The biological results are further compared to the activity of cis-platin.

Graphical abstractIsothiocyanate ligand along with NNO donor tridentate Schiff base ligand with pyrolidine moiety change the geometry of an octahedral NiII complex into square planar one. The reaction pathway has been rationalized by DFT calculation. Bio-activity study reveals that square planar species has higher anticancer activity than the octahedral-species.Figure optionsDownload full-size imageDownload as PowerPoint slide