Nuclear Magnetic Resonance Spectrum of B11 in Inderite

The quadrupolar splitting of the B¹¹ nuclear magnetic resonance signal in a single crystal of inderite Mg₂B₆O₁₁·15H₂O at room temperature has been investigated in a magnetic field of 7187 gauss. The spectra obtained as the crystal was rotated in turn about three mutually perpendicular axes held normal to the magnetic field were interpreted on the basis that the six B¹¹ sites per unit cell belong to three distinct types with the two sites of each type related by a center of symmetry. The electric quadrupole coupling constants C_z and asymmetry parameters η at the three unique B¹¹ sites were determined to be $$\begin{array}{cccc}{C}_z{\mathrm{=eQ\phi }}_{\mathrm{zz}}\mathrm{/h}& \text{355±5\hspace{0.17em}}\mathrm{kc}/\sec & \text{517±7\hspace{0.17em}}\mathrm{kc}/\sec & \text{2546±10\hspace{0.17em}}\mathrm{kc}/\sec \\ {\mathrm{\eta =(\phi }}_{\mathrm{xx}}{\mathrm{-\phi }}_{\mathrm{yy}}{\mathrm{)/\phi }}_{\mathrm{zz}}& \text{0.51±0.03}& \text{0.76±0.01}& \text{0.066±0.003}\end{array}$$ It has been inferred from the foregoing values that two of the boron atoms in the asymmetric unit of inderite have tetrahedral coordinations whereas the third has triangular coordination. The orientations of the principal axes of the electric field gradient tensors at the B¹¹ sites have also been determined.