Five organotin(IV) compounds were synthesized from N'-[(1E)-(2-hydroxy-3-methoxyphenyl)methylidene]
pyridine-4-carbohydrazone and the corresponding dialkyltin(IV) or trialkyltin(IV) precursor. Solid state structures were determined by IR, elemental analysis, NMR spectroscopy, and for 1, 2, 4 and 5 single crystal X-ray diffraction analysis. Compounds 1, 2 and 4 are monomers with the
tin atoms five-coordinated in distorted trigonal bipyramid, of which the deprotonated
Schiff base ligand chelate to
tin center in the enolic tridentate mode. Differently, in compound 5, the enolization does not occur for the
Schiff base ligand, and only the pyridinyl N atom and the deprotonated
phenol hydroxyl oxygen atom participate in the coordination. Fascinatingly, six
trimethyltin(IV) coordination units are linked by the Sn⋯N weak interaction atoms and form a 72-membered crown-like macrocycle. Preliminary in vitro cytotoxicity studies on five human
tumor cells lines (HL-60, A549, HT-29, HCT-116 and Caco-2) by MTT assay reveal that
di-n-butyltin(IV) complex 2 and
diphenyltin(IV) complex 4 triggered significant antiproliferative effects in cultured tumor cells, and their cytotoxic activity correlates with intracellular organotin(IV) concentration. The interaction of the complexes with
calf thymus DNA (CT-
DNA) has been explored by absorption and emission titration methods, which revealed that complexes 2 and 4 interact with CT-
DNA through groove-binding and partial intercalation of the extended planar
ligand with the
DNA base stack. Further, the
albumin interactions of complexes 2 and 4 were investigated using fluorescence quenching spectra and synchronous fluorescence spectra. Studies reveal that
di-n-butyltin(IV) complex 2 with higher cytotoxicity show stronger
DNA/BSA interaction than
diphenyltin(IV) complex 4.