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

Abstract

Six new bicycloazastannoxides of compositions [Me2Sn(L1H)] (1), [nBu2Sn(L1H)] (2), [Ph2Sn(L1H)] (3), [Bz2Sn(L1H)] (4), [Me2Sn(L2H)(MeOH)]·MeOH (5) and [Ph2Sn(L3H)] (6), where L1H = 2-((E)-((Z)-4-hydroxypent-3-en-2-ylidene)amino)-3-(4-hydroxyphenyl)propanoate, L2H = (E)-2-((2-hydroxybenzylidene)amino)-3-(4-hydroxyphenyl)propanoate and L3H = (E)-3-(4-hydroxyphenyl)-2-((1-(2-hydroxyphenyl)ethylidene)amino)propanoate, were synthesized and spectroscopically characterized. The 1H and 13C NMR spectra of compounds 1–6 displayed two sets of signals for Sn-R2 (R = Me, nBu, Ph and Bz) indicating a diastereotopic environment according to the asymmetric nature of the ligand. The 119Sn NMR data of the compounds in CDCl3 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 single 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.