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.

Synthesis and crystal structure of two scandium oxotellurates(IV): Sc2Te3O9 and Sc2Te4O11

The two new scandium oxotellurates(IV) Sc2Te3O9 and Sc2Te4O11 were synthesized through firing appropriate mixtures of Sc2O3, TeO2 and CsBr (as flux) in evacuated glassy silica ampoules at 850 °C for 10 days. Both of them crystallize in the monoclinic space group P21/c with Z = 4 (Sc2Te3O9: a = 523.36(3), b = 2438.23(14), c = 731.98(4) pm, β = 116.221(3)°; Sc2Te4O11: a = 949.51(6), b = 779.12(5), c = 1341.93(9) pm, β = 90.829(3)°). Both crystal structures contain two crystallographically unique Sc3+ cations. In the case of Sc2Te3O9, they reside in six- and sevenfold oxygen coordination arranged as distorted uncapped or capped octahedra, while for Sc2Te4O11, they only exhibit six oxygen atoms in the coordination polyhedra, but one of them has also a certain tendency to thrive for a higher coordination number (C.N. = 6 + 1). The [(Sc1)O6)]9− and [(Sc2)O6+1)]11− polyhedra in Sc2Te3O9 are condensed via common edges to form serrated   ∞ 1 { [ Sc 2 O 6 / 1 t O 1 / 2 v O 4 / 2 e ] 11 − } ${\text{ }}_{\infty }^{1}\left\{{\left[{\text{Sc}}_{2}{\text{O}}_{6\text{/}1}^{\text{t}}{\text{O}}_{1\text{/}2}^{\text{v}}{\text{O}}_{4\text{/}2}^{\text{e}}\right]}^{11-}\right\}$ chains running along [100], whereas the two [ScO6]9− octahedra in Sc2Te4O11 only share common vertices, generating   ∞ 1 { [ Sc 2 O 6 / 1 t O 3 / 2 v ] 9 − } ${\text{ }}_{\infty }^{1}\left\{{\left[{\text{Sc}}_{2}{\text{O}}_{6\text{/}1}^{\text{t}}{\text{O}}_{3\text{/}2}^{\text{v}}\right]}^{9-}\right\}$ double strands along [010]. In both compounds, the three-dimensional framework and the charge balance are accomplished by the discrete ψ1-tetrahedral [TeO3]2− anions with non-bonding lone-pair electrons located at their central Te4+ cations. Moreover, strong secondary Te4+···O2− interactions, which are generally quite common for rare earth metal(III) oxotellurates(IV), occur in both crystal structures, but much more pronounced in Sc2Te4O11, where three quarters of the Te4+ cations reside in the centers of ψ eq 1 ${{\psi}}_{\text{eq}}^{1}$ -trigonal bipyramids [TeO4]4− as compared to Sc2Te3O9, which can well be written as Sc2[TeO3]3.