Self-assembly of organostannoxanes: formation of gels in aromatic solvents

Abstract

Organostannoxane drums [n-BuSn(O)O₂C-C₆H₄-4-OR]₆ [R = -CH₃ (1); -C₉H₁₉ (2); -C₁₁H₂₃ (3)] and [n-BuSn(O)O₂C-C₆H₃-3,5-(OR)₂]6 [R = -CH₃ (4); -C₉H₁₉ (5)] were synthesized by the reaction of n-BuSn(O)(OH) with the corresponding carboxylic acid in a 1:1 stoichiometry. Analogous reactions involving [n-Bu₂SnO]_n in a 1:1 stoichiometry afforded the diorganostannoxane ladders {[n-Bu₂SnO₂C-C₆H₄-4-OR]₂O}₂ [R = -CH₃ (6); -C₉H₁₉ (7); -C₁₁H₂₃ (8)] and {[n-Bu₂SnO₂C-C₆H₃-3,5-(OR)₂]₂O}₂ [R = -CH₃ (9) and -C₉H₁₉ (10)]. Compounds 1-10 could also be prepared by a solventless methodology, which involved grinding the reactants together in a mortar and pestle at room temperature. Compounds 1-10 exhibit gelation behavior in aromatic solvents. In contrast, in aliphatic solvents gelation behavior was not observed. Among the organostannoxanes reported here, 2, 3, 5, and 8 were found to be extremely efficient gelators based on their critical gelation concentration values. The microstructure of the organometallic gels, investigated by optical and scanning electron microscopy, reveals the presence of cross-linked network structures. The gels formed from 2and 3 can be converted into xerogels by removal of solvent. The latter can be reconverted into the original gels by treatment with aromatic solvents.