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Issue 47, 2016
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Structure and thermodynamic stability of UTa3O10, a U(v)-bearing compound

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Heating a mixture of uranyl(VI) nitrate and tantalum(V) oxide in the molar ratio of 2 : 3 to 1400 °C resulted in the formation of a new compound, UTa3O10. The honey colored to yellow brown crystals of UTa3O10 crystallize in an orthorhombic structure with the space group Fddd (no. 70), lattice parameters a = 7.3947(1), b = 12.7599(2), c = 15.8156(2) Å, and Z = 8. Vertex sharing [TaO6]7− octahedra of two crystallographically distinct Ta cations form a three dimensional tantalate framework. Within this framework, six membered rings of [TaO6]7− octahedra are formed within the (001) plane. The center of these rings is occupied by the uranyl cations [UO2]+, with an oxidation state of +5 for uranium. The pentavalence of U and Ta was confirmed by X-ray photoelectron spectroscopy and X-ray adsorption spectroscopy. The enthalpy of formation of UTa3O10 from Ta2O5, β-U3O7, and U3O8 has been determined to be 13.1 ± 18.1 kJ mol−1 using high temperature oxide melt solution calorimetry with sodium molybdate as the solvent at 700 °C. The close to zero enthalpy of formation of UTa3O10 can be explained by closely balanced structural stabilizing and destabilizing factors, which may also apply to other UM3O10 compounds.

Graphical abstract: Structure and thermodynamic stability of UTa3O10, a U(v)-bearing compound

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The article was received on 18 Jul 2016, accepted on 08 Sep 2016 and first published on 09 Sep 2016

Article type: Paper
DOI: 10.1039/C6DT02843H
Dalton Trans., 2016,45, 18892-18899

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    Structure and thermodynamic stability of UTa3O10, a U(V)-bearing compound

    X. Guo, C. Lipp, E. Tiferet, A. Lanzirotti, M. Newville, M. H. Engelhard, D. Wu, E. S. Ilton, S. R. Sutton, H. Xu, P. C. Burns and A. Navrotsky, Dalton Trans., 2016, 45, 18892
    DOI: 10.1039/C6DT02843H

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