Synthesis, Crystal Structure, and Properties of Bi TeBO or Bi (TeO )(BO ): A Non-Centrosymmetric Borate-Tellurate(VI) of Bismuth.

Pale-yellow single crystals of the new borate tellurate(VI) Bi TeBO were obtained by reaction of stoichiometric amounts of Bi O , B O , and Te(OH) at 780 °C. The non-centrosymmetric crystal structure (P6 , Z=2, a=8.7454(16), c=5.8911(11) Å, 738 refl., 43 param, R1=0.037, wR2=0.093) contains isolated trigonal-planar BO units and nearly undistorted TeO octahedra. The Bi cations are located in between in octahedral voids. The BiO octahedra are significantly distorted to a [3+3] pattern (2.25/2.50 Å) due to the ns configuration. According to the structural features, the formula can be written as Bi (TeO )(BO ). Alternatively, the structure can also be described as hcp of oxygen with Te and Bi in octahedral voids and B in trigonal- planar voids. The vibrational spectra show the typical features of BO and TeO units with a significant B/ B isotopic splitting of the IR-active B-O valence mode (1248 and 1282 cm ). The UV/Vis spectrum shows an optical band edge with an onset around 480 nm (2.6 eV). MAS-NMR spectra of B show an anisotropic signal with a quadrupole coupling constant of C =2.55 MHz. and a very small deviation from rotational symmetry (η=0.2). The isotropic chemical shift is 20.1 ppm. The second harmonic generation (SHG) test was positive with an activity comparable to potassium dihydrogen phosphate (KDP). Bi TeBO decomposes in air at 825 °C to Bi TeO .