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

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