B-11 MAS NMR-STUDIES ON THE STRUCTURE OF BORATE ANIONS

The results of B-11 MAS NMR studies on selected crystalline borates and peroxoborates show that the boron coordination number can be determined not only from the quadrupole coupling constant but also from the chemical shift values. Correspondingly, the B[3]: B[4] ratio can be determined quantitatively. In contrast to Al-27, Si-29, and P-31 NMR data, however, the observed small variation of the B-11 chemical shifts does not allow a more detailed information on the linkage of the coordination polyhedra and their environments. The method was applied to Ag borates with unknown structures. In the case of a borate with an Ag:B ratio of 1:3 the measured B[3]:B[4] ratio suggests a triborate structure of the anion.