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

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 P1̅ with Z = 6. The lattice parameters determined at room temperature are a = 1066.42(4) pm, b = 1083.09(4) pm, c = 1560.46(5) pm, α = 98.55(1)°, β = 95.57(1)°, γ = 102.92(1)°, and V = 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.