Molecular aggregations of bicyclodioxazastannone produced from multicomponent reactions involving functionalized 2-hydroxybenzaldehydes, α- or β-amino acids and a dimethyltin precursor

A series of novel bicyclodioxazastannone derived from ONO Schiff base ligands prepared from diazenylaryl functionalized 2-hydroxybenzaldehydes and α or β-amino acetates, viz., [Me2Sn(L1)]2 (1), [Me2Sn(L2)]2 (2), [Me2Sn(L3)(MeOH)]2 (3), [Me2Sn(L4)]n (4), [Me2Sn(L5)]n⋅nH2O (5), [Me2SnL6)]2 (6), [Me2Sn(L7)] (7A), [Me2Sn(L7)]2⋅C8H10 (7B) and [Me2Sn(L8)]n (8), with variously substituted Schiff bases L1-L8 generated in situ, were synthesized and structurally characterized. The crystal structures of compounds 1–8 revealed different structure types with five-, six- or seven-fold coordination of the metal center. Except for 7A, which crystallized in the form of a discrete mononuclear tin complex, intermolecular association through O→Sn interactions was observed. The resulting aggregates were molecular dimers with a central four-membered Sn2O2 ring (1, 2, 6 and 7A), 1D coordination polymers (4, 5 and 8) and a solvent adduct linked through both O–H⋅⋅⋅O hydrogen bonds and O⋅⋅⋅Sn contacts (3). In the presence of hydrogen bond donors such as O–H and N–H groups in the ligands, the molecular structures are further interconnected through O/N–H⋅⋅⋅O hydrogen bonds, giving in combination with the O⋅⋅⋅Sn contacts overall 2D layer-type assemblies. In solution, contrary to the β-alanine derivative 1, the 1H and 13C NMR spectra of compounds 2–8 displayed signals for the Me2Sn moieties because of diastereotopic environments according to the asymmetric nature of the ligand. The 119Sn NMR data of most of the compounds were acquired in DMSO‑d6 with the chemical shift displacements indicating six-coordinate tin atoms, which is in good agreement with the O→Sn adduct formation in the solid-state structures. The 119Sn NMR spectrum of compound 2 measured in CDCl3 indicates the presence of a mononuclear tin complex, as expected for a non-coordinating solvent.