Synthesis and structures of polynuclear organotin(IV) complexes of a polyaromatic carboxylate ligand and cytotoxic evaluation in tumor cell lines

Abstract

Three polynuclear organotin(IV) derivatives of composition [n-Bu3Sn(HL)]n 1, [Ph3Sn(HL)]n 2 and [n-Bu2Sn(HL)2]2 3 were synthesized by reacting 2-((E)-(4-hydroxy-3-((E)-((4-(methoxycarbonyl)phenyl)imino)methyl)phenyl)diazenyl)benzoic acid (H'HL) with (n-Bu3Sn)2O, Ph3SnOH and n-Bu2SnO, respectively. The structures 1–3 were fully characterized by elemental analysis, IR and NMR (1H, 13C, and 119Sn), 119Sn Mössbauer spectroscopy, and additionally, the molecular and crystal structures of 1–3 and its pro-ligand (H'HL) were established by single-crystal X-ray diffraction analysis. The tributyltin(IV) complex 1 is a one-dimensional coordination polymer, in which the azo ligand bridges adjacent Sn(IV) centres solely via the two carboxylate O-atoms. The hydroxy H atom forms an intramolecular O–H···N hydrogen bond with the imine N-atom, as observed in the crystal structure of H'HL. The triphenyltin(IV) complex 2 is also a one-dimensional coordination polymer, but in this case the azo ligand bridges adjacent Sn(IV) centres via its carboxylate group and the deprotonated phenol O-atom. Unlike in 1, the phenol H-atom has migrated to the imine N-atom, to give a zwitterionic form of the azo ligand. The tin centers in 1 and 2 are pentacoordinated and reveal a distorted trans-R3SnO2 trigonal-bipyramidal environment. The dibutyltin(IV) complex 3 crystallizes as discrete centrosymmetric dinuclear entities where the unique Sn(IV) center is heptacoordinated in a distorted pentagonal bipyramid coordination geometry. In vitro cytotoxicity studies of compound 1 were performed and compared with 2 across a panel of human tumor cell lines and the results were compared with the data of six clinically used anticancer drugs. + Graphical abstract