Gaseous Metaborates. II. Infrared Spectra of Alkali Metaborate Vapors

The infrared spectra of gaseous lithium, sodium, and cesium metaborate have been examined between 2500 and 225 cm—1. Bands were observed at 1935 and 600 cm—1 for LiBO2, Li6BO2, NaBO2, and CsBO2, and at 2000 and 610 cm—1 for LiB10O2, NaB10O2 and CsB10O2. The two frequencies have been assigned to a stretching and bending vibration, respectively, of the metaborate BO2 group. Their similarity to the corresponding frequencies of the ion BO2— suggests a bond structure of the form M+(O—–B+–O—) for the alkali metaborates. The variation of the bonding of the BO2 group in a series of related compounds and the absence of alkali—anion stretching frequencies from the spectra of both alkali metaborates and cyanides are also discussed.