First ternary tungsten tellurate(IV) WTe 2 O 7 with unique crystal structure type.

At multianvil high-pressure/high-temperature conditions of 10 GPa and 1273 K, the first ternary tungsten tellurate WTe 2 O 7 is formed, starting from a stoichiometric mixture of WO 3 and TeO 2 . The compound crystallizes triclinic in a hitherto unknown crystal structure type with the space group P 1̄; (no. 2), and was refined from single-crystal X-ray diffractometer data: a = 538.3(1), b = 687.5(1), c = 802.3(1) pm, α = 72.4(1)°, β = 85.7(1)°, γ = 68.1(1)°, w R 2 = 0.0323, GooF = 1.048, 3157 F 2 values, and 106 variables. The main motifs of the crystal structure are pairs of edge-linked [WO 6 ] 6- octahedra and fourfold oxygen-coordinated Te 4+ atoms. The oxidation state of W 6+ and Te 4+ was further verified by measuring the characteristic binding energy values for the W 4f and the Te 3d core levels via X-ray photoelectron spectroscopy (XPS). In addition, DFT calculations of the structure, the associated electron localisation functions (ELF) and vibrational spectra have been carried out. The theoretical data clearly demonstrates the impact of the residual electron density located at the Te 4+ ions, which can be directly interpreted as the presence of lone electron pairs within the solid structure.