11B NMR in Polycrystalline Calcium Metaborate

Boron‐11 nuclear magnetic resonance has been observed in polycrystalline calcium metaborate doped with paramagnetic Mn²⁺. The spectrum arises from the $\mathrm{m\hspace{0.17em}=\hspace{0.17em}}\frac{1}{2}\mathrm{\leftrightarrow m=\hspace{0.17em}-\hspace{0.17em}}\frac{1}{2}$ transition broadened in second order by a quadrupole interaction having a nonzero asymmetry parameter. The quadrupole coupling constant of 2.58 ± 0.02 MHz is consistent with previously published values for three‐coordinated boron. However, the electric field gradient asymmetry parameter of 0.55 ± 0.01 is several times greater than expected, and this large value is attributed to the presence of a nonbridging oxygen in the boron coordination shell. The possibility of using this result for the study of noncrystalline solids is discussed.