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Shape‐Controlled Bridged Silsesquioxanes: Hollow Tubes and Spheres
Author(s) -
Moreau Joël J. E.,
Vellutini Luc,
Wong Chi Man Michel,
Bied Catherine
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200390183
Subject(s) - nucleation , supramolecular chemistry , hybrid material , molecule , hydrogen bond , hydrolysis , intermolecular force , solubility , chemical engineering , crystallography , covalent bond , urea , materials science , chemistry , self assembly , organic chemistry , engineering
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 SiC 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.