First ternary tungsten tellurate(IV) WTe₂O₇ with unique crystal structure type

At multianvil high-pressure/high-temperature conditions of 10 GPa and 1273 K, the first ternary tungsten tellurate WTe₂O₇ is formed, starting from a stoichiometric mixture of WO₃ and TeO₂. The compound crystallizes triclinic in a hitherto unknown crystal structure type with the space group P1̄; (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)°, wR₂ = 0.0323, GooF = 1.048, 3157 F² values, and 106 variables. The main motifs of the crystal structure are pairs of edge-linked [WO₆]^6- octahedra and fourfold oxygen-coordinated Te⁴⁺ atoms. The oxidation state of W⁶⁺ and Te⁴⁺ 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 Te⁴⁺ ions, which can be directly interpreted as the presence of lone electron pairs within the solid structure.