Synthesis, characterisation and biological activities of [(p-cym)RuX(pz4lut)]n+ and [{(p-cym)RuX}2(μ-pz4lut)]n+ (X = Cl, H2O and pz4lut = α,α,α′,α′-tetra(pyrazol-1-yl)-2,6-lutidine)

Mononuclear [(p-cym)RuCl(pz4lut)]Cl (1) and dinuclear [{(p-cym)RuCl}2(μ-pz4lut)]Cl2 (2) complexes (p-cym = 1-isopropyl-4-methylbenzene) comprising of bis(pyrazol-1-yl)methane based heteroscorpionate ligand α,α,α′,α′-tetra(pyrazol-1-yl)-2,6-lutidine (pz4lut) have been synthesised from pz4lut ligand and dimeric precursor complex [(p-cym)RuCl(μ-Cl)]2 in methanol. The aqua derivatives [(p-cym)Ru(H2O)(pz4lut)](ClO4)2 (3) and [{(p-cym)Ru(H2O)}2(μ-pz4lut)](ClO4)4 (4) are obtained from 1 and 2, respectively, via Cl/H2O exchange process in presence of appropriate equivalents of AgClO4 in methanol–water mixture. The molecular structures of dinuclear complexes, 2 and 4 are authenticated by their single crystal X-ray structures. Cyclic voltammetry reveals negligible electronic communication between the metal centres in the ligand bridged complex 2. All four complexes have been tested for their anticancer activities in human breast (MCF7), lung (A549) and colon (HCT116) cancer cell lines. The complexes show dose dependent suppression of cell viability with moderately good IC50 values ranging from 3.5–92 μM. Experimental results have revealed that the aqua derivatives, 3 and 4 exhibit better cytotoxic effect against all those cell lines as compared to the precursor chlorido complexes, 1 and 2. Results also demonstrate that the complexes are more potent against HCT116 cells as compared to other cell lines.