Anionic Dinuclear Oxidovanadium(IV) Complexes with Azo Functionalized Tridentate Ligands and μ-Ethoxido Bridge Leading to an Unsymmetric Twisted Arrangement: Synthesis, X-ray Structure, Magnetic Properties, and Cytotoxicity.

The synthesis of ethoxido-bridged dinuclear oxidovanadium(IV) complexes of the general formula (HNEt3 )[(VOL1-3 )2 (μ-OEt)] (1-3) with the azo dyes 2-(2'-carboxy-5'-X-phenylazo)-4-methylphenol (H2 L1 , X = H; H2 L2 , X = NO2 ) and 2-(2'-carboxy-5'-Br-phenylazo)-2-naphthol (H2 L3 ) as ligands is reported. The ligands differ in the substituents at the phenyl ring to probe their influence on the redox behavior, biological activity, and magnetochemistry of the complexes, for which the results are presented and discussed. All synthesized ligands and vanadium(IV) complexes have been characterized by various physicochemical techniques, namely, elemental analysis, electrospray ionization mass spectrometry, spectroscopic methods (UV/vis and IR), and cyclic voltammetry. X-ray crystallography of 1 and 3 revealed the presence of a twisted arrangement of the edged-shared bridging core unit. In agreement with the distorted nature of the twisted core, antiferromagnetic exchange interactions were observed between the vanadium(IV) centers of the dinuclear complexes with a superexchange mechanism operative. These results have been verified by DFT calculations. The complexes were also screened for their in vitro cytotoxicity against HeLa and HT-29 cancer cell lines. The results indicated that all the synthesized vanadium(IV) complexes (1-3) were cytotoxic in nature and were specific to a particular cell type. Complex 1 was found to be the most potent against HeLa cells (IC50 value 1.92 μM).