The High-pressure Thallium Triborate HP-TlB3O5
2015
Sohr, Gerhard | Perfler, Lukas | Huppertz, Hubert
The thallium triborate HP-TlB₃O₅ (HP=high-pressure) was synthesized in a Walker-type multianvil apparatus under high-pressure=high-temperature conditions of 6 GPa and 1400°C. A mixture of thallium carbonate Tl₂CO₃ and boric acid H₃BO₃ initially heated at 850°C under ambient-pressure conditions was used as a precursor for the high-pressure experiment. Single-crystal X-ray diffraction data revealed that HP-TlB₃O₅ is isotypic to HP-M′B₃O₅ (M′ =K, Rb). Furthermore the B-O network is identical to the substitutional variants HP-M″B₃O₅ [M″ =Cs₁₋ₓ(H₃O)x (x=0.5 - 0.7), NH₄]. HP-TlB₃O₅ crystallizes with eight formula units (Z =8) in the monoclinic space group C2=c (no. 15). The lattice parameters are a=996.3(2), b=884.0(2), c=913.1(2) pm, β =103:3(1)°, and V =782.5(3) ų. Trigonal-planar BO₃ groups, corner-sharing BO₄ tetrahedra, and B₂O₆ groups consisting of two edge-sharing BO₄ tetrahedra are present in the structure, forming a three-dimensional network. The thallium ions are located in channels of the boron-oxygen network being tenfold coordinated by oxygen atoms and do not show any lone pair effect at all. IR and Raman spectroscopic investigations were performed on single crystals of the compound.
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