High-molecular-weight boron oxides in the gas phase

Abstract

A new class of gas-phase boron oxides has been produced by particle-induced desorption from vitreous boron trioxide. Six distinct homologous series of boron oxide cations were identified by fast atom bombardment mass spectrometry and studied by collision-induced dissociation. Common structural features within each series were confirmed by the identification of common collision-induced fragments. Two important series are described by the general formulas (B/sub 2n+1/O/sub 3n+1/)/sup +/ (n = 0.6) and (B/sub 2n+2/O/sub 3n+3/)/sup center dot +/ (n = 0-4). Ions of the first series show the highest relative abundance in the desorption spectrum of boron trioxide and are the most abundant ionic fragments in the collision spectra of nearly all boron oxide cations. The most important of these is (B/sub 2/O/sub 4/)/sup +/, which is proposed to exist as (O/double bond/B/emdash/O/emdash/B/emdash/O/emdash/B/double bond/)/sup +/ and is stabilized by extensive resonance and electron sharing. Gas-phase boron oxide cations are proposed to exist with boron limited to two- or three-coordination with oxygen. The ions are thus built upon integral BO/sub 3/ triangles, and branches are terminated with -B/double bond/O units.