Synthesis and characterization of bis[dicarboxylatotetraorganodistannoxane] units involving 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoic acids: An investigation of structures by X-ray diffraction, NMR, electrospray ionisation MS and assessment of in vitro

Reactions of 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoic acids (LHH′, where the aryl group is an R-substituted phenyl ring such that for L1HH′: R = H; L2HH′: R = 2′-CH3; L3HH′: R = 3′-CH3; L4HH′: R = 4′-CH3; L5HH′: R = 4′-Cl; L6HH′: R = 4′-Br) with nBu2SnO in a 1:1 molar ratio yielded complexes of composition {[nBu2Sn(LH)]2O}2. The complexes have been characterized by 1H, 13C, 119Sn NMR, ESI-MS, IR and 119mSn Mössbauer spectroscopic techniques in combination with elemental analyses. The crystal structures of {[nBu2Sn(L1H)]2O}2 (1), {[nBu2Sn(L4H)]2O}2 (4), {[nBu2Sn(L5H)]2O}2 (5) and {[nBu2Sn(L6H)]2O}2 (6) were determined. The compounds are centrosymmetric tetranuclear bis(dicarboxylatotetrabutyldistannoxane) complexes containing a planar Sn4O2 core in which two μ3-oxo O-atoms connect an Sn2O2 ring to two exocyclic Sn-atoms. The four carboxylate ligands display two different modes of coordination where both modes involve bridging of two structurally distinct Sn-atoms. The solution structures were confirmed by 119Sn NMR spectroscopy by observing two tin resonances in compounds 1, and 4–6. The observed difference between the two tin resonances was about 3 ppm while the differences in 13C resonances were even smaller. Compounds {[nBu2Sn(L2H)]2O}2 (2) and {[nBu2Sn(L3H)]2O}2 (3) undergo a very complex exchange processes in deuteriochloroform solution. The in vitro cytotoxic activity of compounds 1 and 4 against WIDR, M19 MEL, A498, IGROV, H226, MCF7 and EVSA-T human tumour cell lines is reported.