Tungstate bronze (TB) related borate–phosphate K5Ta8BP4O34 is afforded from boron-enriched potassium–molybdate flux. It was found to crystallize [space group P2/c (no. 13), a = 1384.36(5), b = 640.99(2), c = 2054.75(8) pm, β = 125.007(2)°, V = 1493.44(9) × 106 pm3] isotypically with the K5MIV2Nb6P5O34 (M = Ti, Zr) group of compounds. Revealed by X-ray structural analysis, occupational disorder of boron and phosphorus atoms over two crystallographically distinct positions was explained by the decrease of tetrahedral distortions. The calculated electronic structure of title compound was found to be similar to that reported for UV-Vis active niobium phosphate photocatalysts for full water decomposition. Transformation of the parental [Ta8BP4O34] framework at incongruent melting (T = 1618 K) into MIMI′2MV6P3O24-type phosphates was detected leading to a subtle structural relationship of phosphates bearing TB building features.

Peer reviewed