VIBRATIONAL-SPECTRUM OF TRISODIUM CALCIUM PENTABORATE NA3CA(B5O10) AND PROBABLE OCCURRENCE OF THE DISCRETE PENTABORATE ION (B5O10)(5-) IN SOME GLASSY METABORATES

The IR and Raman spectra of the discrete pentaborate ion (B5O10)(5-) ( existing in the compound Na3CaB5O10) are presented and discussed in re lation with the possible existence of this ion in some glasses with (o r near) a metaborate composition. The existence of the discrete pentab orate ion in glasses is supported by the strong analogy between the IR spectra of crystalline and vitreous Na3CaB5O10. Likewise, the Raman s pectrum of crystalline Na3CaB5O10 exhibits. at 576 cm(-1), a character istic very strong, sharp peak, which is also present in the Raman spec tra of glassy metaborates M(+)BO(2) (M(+) = Na...Cs) published in the literature. It is inferred that the discrete pentaborate ion (B5O10)(5 -) can be one of the structural units existing in such glasses. This i on disappears rapidly and is replaced by other structural units 1) whe n the cation/anion ratio is significantly different from that of the m etaborate composition: 2) when, for a metaborate composition. the chem ical nature of the cations is such that the cation-oxygen bonds are no t strongly ionic.