Synthesis, structural characterization and DNA-binding properties of organotin(IV) complexes based on Schiff base ligands derived from 2-hydroxy-1-naphthaldy and 3- or 4-aminobenzoic acid

Six organotin(IV) complexes {p-[C10H6(OH)CHdouble bond; length as m-dashN]–(C6H4)CO2}2Sn(n-Bu)2 (1), {{p-[C10H6(O−)CHdouble bond; length as m-dashN+H]–(C6H4)CO2}SnMe3}∞ (2), {{p-[C10H6(O−)CHdouble bond; length as m-dashN+H]–(C6H4)CO2} SnPh3}∞·CH2Cl2 (3), {{m-[C10H6(OH)CHdouble bond; length as m-dashN]–(C6H4)CO2}2[Sn(n-Bu)2]2O}2·CH2Cl2·CH3OH (4), {m-[C10H6(O)CHdouble bond; length as m-dashN]–(C6H4)(CO2)2][(C10H6)CHdouble bond; length as m-dashN(C6H4)]O}Sn(n-Bu)2(CH3CH2OH) (5), {{m-[C10H6(O−)CHdouble bond; length as m-dashN+H]–(C6H4)CO2}SnMe3}∞ (6) have been synthesized by the reaction of organotin(IV) chlorides with Schiff base ligands derived from 2-hydroxy-1-naphthaldehyde and 4-aminobenzoic acid (or 3-aminobenzoic acid). All complexes have been characterized by elemental analyses, 1H, 13C, 119Sn NMR, IR, UV–Vis spectroscopy and X-ray single crystal diffraction. In these complexes, Schiff bases coordinated to metal ion through carboxylate O atom and the hydroxyl O atom. In complexes 1 and 4, Schiff base ligands only present bidentate coordination modes with the carboxylate O atoms binding to the tin center. However, in the complex 5, tin atom is surrounded by three Schiff base ligands through hydroxyl O-atom and carboxylate O atom. To the best of our knowledge, the structure like complex 5 has been rarely reported. The crystal structures of complexes 2, 3 and 6 reveal that they exist as polymeric zig-zag chains in which the LH-bridged tin atoms adopt a trans-R3SnO2 trigonal bipyramidal configuration. The DNA-binding properties of complexes 1–6 with calf thymus DNA (CT-DNA) have also been investigated by fluorescent spectra, and results indicate that the complexes 1–6 can bind to CT-DNA via an intercalative mode.