Hexabromodisilane reacts with sulphur trioxide at room temperature to give pure silicon sesquioxide in almost quantitative yield, together with bromine and sulphur dioxide as the only by-products.During the course of our investigations with hexahalogenodisilanes we observed that hexabromodisiiane reacted with sulphur trioxide at room temperature to give a white amorphous solid containing intact Si-Si bonds. The solid was found to be silicon sesquioxide, Si2O3 (m.p. 1 635 "C, surface area 50-60 m2 g-', apparent density 0.16--0.22 g cm-j), previously prepared by a high-temperature method which involved heating silicon oxyhydride (Si2H203) in an inert atmosphere at 900 "C. The present method is much simpler, occurs at room temperature, and the reaction goes to completion.

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Stable solid adducts of SiF4 with the following aminocyclophosphazenes have been synthesized : N3P3(NHCH2CH2NH)(NMe2)4, (1) ; N3P3(NHCH2CH2NH)C14, (2) ; N3P3(NMe2)4C12, (3) ; N3P3(NHMe),, (4) ; N3P3(NMe2),, (5) ; N,P,(NHMe),, (6) ; N4P4(NMe2),, (7) ; and N,P,(NHBu' ),, (8). They have been characterized by elemental analysis, i.r., and n.m.r. ( H, 31 P, and 19F) spectroscopy. The composition of the adducts varies depending on the ring size and also on the nature of the substituents on the phosphorus. The number of SiF4 molecules accommodated by the ligands is larger when the ring size is large, while it is less when the ligands contain chlorine. Except in the cases of ligands ( 1) and (2), bonding is through the ring nitrogens. With ( I ) , both exocyclic nitrogen and ring nitrogen atoms, and with (2) only exocyclic nitrogen atoms, participate in co-ordination. In these two cases the silicon is six-co-ordinated, while in the other cases it is five-co-ordinated.Silicon tetrafluoride, a good Lewis acid, is known to form stable adducts with a variety of donor groups such as amines and a few with oxygen donor^.^-^ There is not much information about adducts with ligands containing phosphorus and also with multidentate ligands containing more than two donor sites. The only relevant work is that of Beattie and Ozin who obtained addition compounds, SiF4*PMe3 and SiF4-2PMe3, at low temperature. However, no adduct formation has been observed between silicon tetrafluoride and triphenylphosphine even when the reactants are cooled to -96 oC.6 Therefore, it was of interest to see whether aminocyclophosphazenes, which behave as potential ligands towards suitable electron acceptors, having donor sites at ring nitr~gen,~ exocyclic nitr~gen,~ and phosphorus,8 would bond with silicon tetrafluoride. Preliminary studies indicated reaction with the eight cyclophosphazenes studied.