The High-pressure Thallium Triborate HP-TlB3O5

Abstract

Abstract 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) Å3. 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.