Nuclear Quadrupole Interaction of ²³Na and ¹¹B and the Crystal Structure of NaBF₄

The nuclear quadrupole interaction of 23 Na and 11 B in NaBF 4 is investigated between 23 and 260 °C using single crystals and crystalline powder respectively. At 23 °C the following results are found: e 2 q Q/h ( 23 Na) = 1008.4kHz; e 2 q Q/h ( 11 B) = 59.9 kHz; η (Na) = 0.095; η (B) = 0.65. The crystal structure is as follows: Space group Cmcm; a = 6.841 Å, b = 6.266 Å, c = 6.799 Å; Z = 4; Na and B in (4c) with y (Na) = 0.656; y (B) = 0.161; F(I) in (8 f) with y = 0.290; z = 0.086; F(II) in (8 g) with x = 0.163; y = 0.032. The point charge model, NMR‐investigation and the crystal structure agree well assuming a 55% ionic character for the B‐F bond. The high temperature phase of NaBF 4 (between 250 and 260 °C) has non‐cubic point symmetry of the B: e 2 q Q/h ( 11 B) = 34 kHz.