title: Shape-controlled bridged silsesquioxanes: hollow tubes and spheres.
abstract: A new approach for the morphological control of bridged silsesquioxanes has been achieved by the hydrolysis of silylated organic molecules bearing urea groups. The urea groups are responsible for the auto-association of the molecules through intermolecular hydrogen-bonding interactions. The self-assembly leads to supramolecular architectures that have the ability to direct the organization of hybrid silicas under controlled hydrolysis. The hydrolysis of the chiral diureido derivatives of trans-(1,2)-diaminocyclohexane 1 under basic conditions has been examined. The solid-state NMR spectra ((29)Si and (13)C) showed the hybrid nature of these materials with wholly preserved S-C bond covalent bonds throughout the silicate network. Hybrid silicas with hollow tubular morphologies were obtained by the hydrolysis of the enantiomerically pure compounds, (R,R)-1 or (S,S)-1, whereas the corresponding racemic mixture, rac-1, led to a hybrid with ball-like structures. The tubular shape is likely to result from a combination of two phenomena: the auto-association abilities and a self-templating structuration of the hybrid materials by the organic crystalline precursor. Electronic microscopy techniques (SEM and TEM) gave evidence for the self-templating pathway. The formation of the ball-like structures occurs through a usual nucleation growth phenomenon owing to a higher solubility of the corresponding crystals in the same medium.
authors.affiliation: Hétérochimie Moléculaire et Macromoléculaire (UMR-CNRS 5076), Ecole Nationale Supérieure de Chimie de Montpellier, France. jmoreau@cit.enscm.fr
authors.forename: Joël J E
authors.initials: JJ
authors.lastname: Moreau
authors.forename: Luc
authors.initials: L
authors.lastname: Vellutini
authors.forename: Michel
authors.initials: M
authors.lastname: Wong Chi Man
authors.forename: Catherine
authors.initials: C
authors.lastname: Bied