Synthesis, characterization, crystal structures and supramolecular features of bicycloazastannoxides derived from Schiff bases with L-tyrosine

Six new bicycloazastannoxides of compositions [Me 2 Sn(L 1 H)] (1), [nBu 2 Sn(L 1 H)] (2), [Ph 2 Sn(L 1 H)] (3), [Bz 2 Sn(L 1 H)] (4), [Me 2 Sn(L 2 H)(MeOH)]·MeOH (5) and [Ph 2 Sn(L 3 H)] (6), where L 1 H = 2-((E)-((Z)-4-hydroxypent-3-en-2-ylidene)amino)-3-(4-hydroxyphenyl)propanoate, L 2 H = (E)-2-((2-hydroxybenzylidene)amino)-3-(4-hydroxyphenyl)propanoate and L 3 H = (E)-3-(4-hydroxyphenyl)-2-((1-(2-hydroxyphenyl)ethylidene)amino)propanoate, were synthesized and spectroscopically characterized. The 1 H and 13 C NMR spectra of compounds 1–6 displayed two sets of signals for Sn-R 2 (R = Me, nBu, Ph and Bz) indicating a diastereotopic environment according to the asymmetric nature of the ligand. The 119 Sn NMR data of the compounds in CDCl 3 indicate five-coordinate tin atoms, showing that the bicycloazastannoxide assemblies remain intact as observed in the solid-state structures. The crystal structures of 1–6 revealed discrete molecular structures in all cases with distorted trigonal-bipyramidal geometries for 1–4 and 6, and a strongly distorted six-fold coordination for 5 due to association of a MeOH solvent molecule. At the supramolecular level, the molecular structures in 1–4 and 6 are linked either through double-bridged O-H⋯O/C-H⋯O synthons (1 and 6) or s ingle O-H⋯O hydrogen bonds (2–4). The resulting 1D helical strands exhibit varying Sn⋯Sn distances due to the different molecular conformations. The molecules in 5 associate to dimers through two Sn⋯O and O-H⋯O interactions, which are further connected via O-H⋯O hydrogen bonds to give 1D strands containing 22-membered macrocycles.