Binuclear Ni(II) complexes containing ONS donor Schiff base ligands: Preparation, spectral characterization, X-ray crystallography and biological exploration.

Four binuclear Ni(II) complexes [[Ni(H-DEAsal-tsc)(μ-dppm)]·2Cl (1), [Ni(DEAsal-mtsc)(μ-dppm)] (2), [Ni(DEAsal-etsc)(μ-dppm)] (3) and [Ni(DEAsal-ptsc)(μ-dppm)] (4)] were synthesized from the ligands namely 4(N,N)-diethylaminosalicylaldehyde-4(N)-thiosemicarbazone [H-DEAsal-tsc] HL/4(N,N)-diethylaminosalicylaldehyde-4(N)-methyl thiosemicarbazone [H-DEAsal-mtsc] HL/4(N,N)-diethylaminosalicylaldehyde-4(N)-ethyl thiosemicarbazone [H-DEAsal-etsc] HL/4(N,N)diethylaminosalicylaldehyde-4(N)-phenyl thiosemicarbazone [H-DEAsal-ptsc] HL and 1,1'-bis(diphenylphosphino)methane (dppm) and characterized by a number of spectro analytical techniques. The molecular structure of complexes [Ni(H-DEAsal-tsc)(μ-dppm)]·2Cl (1) and [Ni(DEAsal-ptsc)(μ-dppm)] (4) have been confirmed by single crystal X-ray diffraction studies. The analysis indicated that in complex 1, the ligand [H-DEAsal-tsc] coordinated as monobasic tridentate donor through phenolic oxygen, azomethine nitrogen and thione sulfur atoms. However, in complex 4, the ligand [H-DEAsal-ptsc] behaved as dibasic tridentate donor with thiolate sulfur coordination. Their ability to bind with Calf Thymus Deoxyribonucleic acid (CT-DNA) and Bovine Serum Albumin (BSA) were analysed spectrometrically. Intercalative interaction of the complexes with DNA was confirmed by ethidium bromide (EB) displacement studies and DNA viscosity measurements. The interaction mechanism of the complexes with BSA was found as static. In vitro antiproliferative studies of the ligands and complexes in A549 (human lung carcinoma cancer), MCF-7 (human breast cancer) and HeLa (human cervical cancer) cell lines witnessed significant cytotoxic nature of the complexes with low IC values (in μM) than the standard metallo-drug cisplatin. Further, the results of Lactate Dehydrogenase (LDH) and Nitric oxide (NO) release assays supported the effectiveness of the complexes on the above said cancer cells.