Structural Redetermination and Photoluminescence Properties of the Niobium Oxyphosphate (NbO)₂P₄O₁₃

Abstract

The structure of (NbO)₂P₄O₁₃ was solved and refined based on new single-crystal diffraction data revealing considerably more complexity than previously described. (NbO)₂P₄O₁₃ crystallizes in the triclinic space group <i>P</i>1̅ with <i>Z</i> = 6. The lattice parameters determined at room temperature are <i>a</i> = 1066.42(4) pm, <i>b</i> = 1083.09(4) pm, <i>c</i> = 1560.46(5) pm, α = 98.55(1)°, β = 95.57(1)°, γ = 102.92(1)°, and <i>V</i> = 1.7213(2) nm³. The superstructure contains 64 unique atoms including two disordered semioccupied oxygen positions. An unusual 180° bond angle between two [P₄O₁₃]^6– groups was refined to form half-occupied, split positions in agreement with previous reports. The IR and Raman spectra reflect the appearance of overlapping bands assignable to specific group vibrations as well as P–O–P linkages present in the [P₄O₁₃]^6– entities. Investigation of the powdered product concerning its photoluminescence properties revealed an excitability in the UV at 270 nm assigned to O2p–Nb4d charge transfer transitions. A resulting broad-band emission with the maximum in the visible region at 455 nm was determined