Dibutyltin(IV) complexes of the 5-[( E)-2-(Aryl)-1-diazenyl]-2-hydroxybenzoic acid ligand: an investigation of structures by X-ray diffraction, solution and solid state tin NMR, electrospray ionisation MS and assessment of in vitro cytotoxicity

Abstract

A series of dibutylbis{5-[( E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoato}tin(IV) complexes, Bu 2Sn(LH) 2, have been prepared and characterized by 1H, 13C, 119Sn NMR and ESI mass spectrometry in solution. The structures of the complexes Bu 2Sn(L 1H) 2 ( 1), Bu 2Sn(L 3H) 2 ( 3), Bu 2Sn(L 4H) 2 ( 4), and Bu 2Sn(L 6H) 2 ( 6) (L = 5-[( E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoate: aryl = phenyl (L 1H), 3-methylphenyl (L 3H), 4-methylphenyl (L 4H) and 4-bromophenyl (L 6H)) were determined by X-ray crystallography and 117Sn CP-MAS NMR spectroscopy in the solid state. In general, the complexes were found to adopt a skew-trapezoidal bipyramidal arrangement around the tin atom. In addition, there are weak bridging intermolecular Sn⋯O contacts in complexes 1 and 3, but not in 4 and 6, where one of the hydroxy oxygen atoms from a neighboring molecule coordinates weakly with the Sn atom, thereby completing a seventh coordination site in the extended Sn coordination sphere. The Sn⋯O distance is 3.080(2) and 3.439(2) Å in 1 and 3, respectively, which are significantly shorter than the sum of the van der Waals radii of the Sn and O atoms (∼3.8 Å). In 1, this Sn⋯O interaction links the molecules into polymeric chains. In 3, these interactions link pairs of molecules into head-to-head dimeric units. The in vitro cytotoxicity of compound 2 indicates better results than cisplatin and etoposide against seven well characterized human tumor cell lines.