Synthesis, crystal structures, cytotoxicity and qualitative structure–activity relationship (QSAR) of cis-bis{5-[(E)-2-(aryl)-1-diazenyl]quinolinolato}di-n-butyltin(IV) complexes, nBu2Sn(L)2

A series of cis-bis{5-[(E)-2-(aryl)-1-diazenyl]quinolinolato}di-n-butyltin(IV) complexes has been synthesized and characterized by 1H-, 13C-, 119Sn NMR, ESI–MS (electrospray ionization mass spectrometry), IR and 119mSn Mössbauer spectroscopic techniques in combination with elemental analyses. The structures of four di-n-butyltin(IV) complexes, viz., nBu2Sn(L3)2 (3), nBu2Sn(L4)2 (4), nBu2Sn(L5)2 (5) and nBu2Sn(L7)2 · 0.5C6H6 (7) (LH = 5-[(E)-2-(aryl)-1-diazenyl)quinolin-8-ol) were determined by single crystal X-ray diffraction. In general, the complexes were found to adopt a distorted cis-octahedral arrangement around the tin atom. These complexes retain their solid-state structure in non-coordinating solvent as evidenced by 119Sn and 13C NMR spectroscopic results. The in vitro cytotoxicity of di-n-butyltin(IV) complexes (3–8) is reported against seven well characterized human tumour cell lines. The basicity of the two quinolinolato donor N and O atoms of the ligands are discussed in relation to the cytotoxicity data.