Synthesis and structural characterization of a remarkably stable, anionic, incompletely condensed silsesquioxane framework

The reaction of [(C6H11)(7)Si7O9(OH)(3)] 1 (2 equiv,) with [(C6H11)(7)Si7O9(OTl)(3)] 3 affords a conproportionation product that reacts with [PPh4]Cl, [PBu4n]Cl and [NBu4n]Br to produce the corresponding salts of [(C6H11)(7)Si7O10(OH)(2)](-) 5 (i.e. the monoanion derived from deprotonation of 1); a single-crystal X-ray diffraction study of the [(NBu4n](+) salt of 5 indicates that the molecules exist as isolated ion pairs with strong intramolecular hydrogen bonding; implications of this result for the chemistry of silica are discussed.