Synthesis, Crystal Structure, and Properties of Bi3TeBO9 or Bi3(TeO6)(BO3): A Non-Centrosymmetric Borate-Tellurate(VI) of Bismuth

Pale-yellow single crystals of the new borate tellurate(VI) Bi3TeBO9 were obtained by reaction of stoichiometric amounts of Bi2O3, B2O3, and Te(OH)(6) at 780 degrees C. The non-centrosymmetric crystal structure (P6(3), Z= 2, a= 8.7454(16), c= 5.8911(11) angstrom, 738 refl., 43 param, R1= 0.037, wR2= 0.093) contains isolated trigonal-planar BO3 units and nearly undistorted TeO6 octahedra. The Bi3+ cations are located in between in octahedral voids. The BiO6 octahedra are significantly distorted to a [3+3] pattern (2.25/2.50 angstrom) due to the ns2 configuration. According to the structural features, the formula can be written as Bi-3 (TeO6)(BO3). Alternatively, the structure can also be described as hcp of oxygen with Te-VI and Bi-III in octahedral voids and B-III in trigonal-planar voids. The vibrational spectra show the typical features of BO3 and TeO6 units with a significant B-10/ B-11 isotopic splitting of the IR-active B-O valence mode (1248 and 1282 cm(-1)). The UV/Vis spectrum shows an optical band edge with an onset around 480 nm (2.6 eV). MAS-NMR spectra of B-11 show an anisotropic signal with a quadrupole coupling constant of C-Q= 2.55 MHz. and a very small deviation from rotational symmetry (eta= 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). Bi3TeBO9 decomposes in air at 825 degrees C to Bi2TeO5.