Rich Non-centrosymmetry in a Na–U–Te Oxo-System Achieved under Extreme Conditions

Abstract

Two new sodium uranyl tellurites and two new sodium uranyl tellurates have been synthesized from high-temperature/high-pressure conditions and structurally characterized. We demonstrated that crystalline phases, forming in a Na-U-Te system under extreme conditions, appear to favorably have non-centrosymmetric structures. Three out of four novel uranyl tellurium compounds, Na[(UO2)Te(IV)2O5(OH)], Na2[(UO2)(Te(VI)2O8)], and Na2[(UO2)Te(VI)O5], crystallize in non-centrosymmetric space groups. The crystal structure of Na[(UO2)Te(IV)2O5(OH)] is based on two-dimensional [UO2Te2O5(OH)](-) corrugated sheets, which are charge balanced by guest Na(+) cations. The structure of Na2[(UO2)Te(VI)2O8] is constructed from [(UO2)2Te2O8](2+) anionic layers composed of UO7 pentagonal bipyramids and TeO6 octahedra. Na2[(UO2)(Te(VI)O5)] is a new type of three-dimensional anionic open framework built from the interconnection of UO7 pentagonal bipyramids and TeO6 octahedra with different types of interlacing channels within the U-Te anionic framework. Na[(UO2)Te(IV)6O13(OH)], as the only centrosymmetric compound isolated in the Na-U-Te family, is crystallized in space group Pa3̅, and its structure is highly related to that of cliffordite (UO2(Te3O7)), which is composed from UO8 hexagonal bipyramids and TeO5 square pyramids. The vibrational modes associated with U-O, Te(IV)-O, and Te(VI)-O bonds are discussed, and the Raman spectra of the four compounds are characterized for signature bands.

Mild Periodic Acid Flux and Hydrothermal Methods for the Synthesis of Crystalline f-Element-Bearing Iodate Compounds

“…In addition, molten salt flux was extensively introduced to the field of actinide solid-state chemistry, emphasizing understanding the structure property relationship in salt-inclusion uranyl silicates that is directly involved in the radioactive waste storage forms . High-temperature reactions with controllable pressure produced a series of actinide oxoanion compounds featured with more complex structural architecture than those compounds obtained from traditional methods . Inspired by these results, periodic acid was chosen for its low melting point of 128.5 °C.…”

Structural and Spectroscopic Investigation of Novel 2D and 3D Uranium Oxo-Silicates/Germanates and Some Statistical Aspects of Uranyl Coordination in Oxo-Salts

“…29 For the U− As Recently, we found that high-temperature/highpressure conditions increase the diversity of U−Se/Te 4+ −O frameworks due to the variation of coordination geometries of Te 4+ and U 6+ . 33,34 The average CN of U for U−Se/Te 4+ −O family (5.04) is close to that for U−P/As 3+ −O, which is attributed to the same ionic potential (0.06) for both systems. By analyzing the coordination environments of uranyl ions in all known U 6+ −T−O phases, we found that the ionic potential of central cations T in oxo-anion groups in their higher oxidation states correlates to the CNs of uranyl ions in these materials.…”

“…Almost half of the structures for the U–Se/Te 4+ –O system have 5-coordinated uranyl, and structures of 10 phases possess mixed 4- and 5-coordinated and 5- and 6-coordinated uranyls. Recently, we found that high-temperature/high-pressure conditions increase the diversity of U–Se/Te 4+ –O frameworks due to the variation of coordination geometries of Te 4+ and U 6+ . , The average CN of U for U–Se/Te 4+ –O family (5.04) is close to that for U–P/As 3+ –O, which is attributed to the same ionic potential (0.06) for both systems.…”

Thorium Chemistry in Oxo-Tellurium System under Extreme Conditions

“…The Te VI is found in both cation-involved phases, even though Na 4 Th 2 ­(Te VI 3 O 15 ) was synthesized from the TeO 2 as the starting chemical. This might suggest that the sealed-condition environment with the presence of oxo nitrates could drive the valence transition from Te IV to Te VI . , …”