Dinuclear Face-Sharing Bi-octahedral Tungsten(VI) Core and Unusual Thermal Behavior in Complex Th Tungstates

Expansion of the structural diversity of f-element bearing molybdate iodates: synthesis, structures, and optical properties

Expanding the family of f-element bearing molybdate iodates has resulted in eleven new complexes with periodically evolved topologies and intriguing optical properties.

Investigation of reactivity and structure formation in a K-Te-U oxo-system under high-temperature/high-pressure conditions

The high-temperature/high-pressure treatment of the K-Te-U oxo-family at 1100 °C and 3.5 GPa results in the crystallization of a series of novel uranyl tellurium compounds, K₂[(UO₂)₃(Te^IVO₃)₄], K₂[(UO₂)TeO₁₄], α-K₂[(UO₂)Te^VIO₅] and β-K₂[(UO₂)Te^VIO₅]. In contrast to most of the reported uranyl compounds which are favorable in layered structures, we found that under extreme conditions, the potassium uranyl oxo-tellurium compounds preferably crystallized in three-dimensional (3D) framework structures with complex topologies. Anion topology analysis indicates that the 3D uranyl tellurite anionic framework observed in K₂[(UO₂)₃(Te^IVO₃)₄] is attributable to the additional linkages of TeO₃ polyhedra connecting with TeO₄ disphenoids from the neighboring U-Te layers. The structure of K₂[(UO₂)TeO₁₄] can be described based on [UTe₆O₂₆]^22- clusters, where six TeO₅ polyhedra enclose a hexagonal cavity in which a UO₈ polyhedron is located. The [UTe₆O₂₆]^22- clusters are further linked by TeO₅ square pyramids to form the 3D network. Similar to uranyl tellurates, both α-K₂[(UO₂)Te^VIO₅] and β-K₂[(UO₂)Te^VIO₅] contain TeO₆ octahedra which share a common face to form a dimeric Te₂O₁₀ unit. However, in α-K₂[(UO₂)Te^VIO₅], these Te₂O₁₀ units connect with UO₆ tetragonal bipyramids to form a 3D structural framework, while in β-K₂[(UO₂)Te^VIO₅], the same Te₂O₁₀ dimers are observed to link with UO₇ pentagonal bipyramids, forming 2D layers. Raman measurements were carried out and the vibration bands related to Te^IV-O, Te^VI-O and U^VI-O bonds are discussed.

Thorium Chemistry in Oxo-Tellurium System under Extreme Conditions

Through the use of a high-temperature/high-pressure synthesis method, four thorium oxo-tellurium compounds with different tellurium valence states were isolated. The novel inorganic phases illustrate the intrinsic complexity of the actinide tellurium chemistry under extreme conditions of pressure and temperature. Th₂Te₃O₁₁ is the first instance of a mixed-valent oxo-tellurium compound, and at the same time, Te exhibits three different coordination environments (Te^IVO₃, Te^IVO₄, and Te^VIO₆) within a single structure. These three types of Te polyhedra are further fused together, resulting in a [Te₃O₁₁]^8- fragment. Na₄Th₂(Te^VI₃O₁₅) and K₂Th(Te^VIO₄)₃ are the first alkaline thorium tellurates described in the literature. Both compounds are constructed from ThO₉ tricapped trigonal prisms and Te^VIO₆ octahedra. Na₄Th₂(Te^VI₃O₁₅) is a three-dimensional framework based on Th₂O₁₅ and Te₂O₁₀ dimers, while K₂Th(Te^VIO₄)₃ contains tungsten oxide bronze like Te layers linked by ThO₉ polyhedra. The structure of β-Th(Te^IVO₃)(SO₄) is built from infinite thorium chains cross-linked by Te^IVO₃^2- and SO₄^2- anions. Close structural analysis suggests that β-Th(Te^IVO₃)(SO₄) is highly related to the structure of α-Th(SeO₄)₂. Additionally, the Raman spectra are recorded and the characteristic peaks are assigned based on a comparison of reported tellurites or tellurates.

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

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.

Effects of Te(IV) Oxo-Anion Incorporation into Thorium Molybdates and Tungstates

The exploration of phase formation in the Th-Mo/W-Te systems has resulted in four mixed oxo-anion compounds from high-temperature solid-state reactions: ThWTe2O9, Th(WO4)(TeO3), ThMoTe2O9, and Th2(MoO4)(TeO3)3. All four compounds contain edge-sharing thorium polyhedra linked by MoO4/WO6 and different tellurium oxo-groups to form three-dimensional frameworks. In ThWTe2O9, each helical Th based chain is connected by four tungstotellurite clusters resulting in a building fragment which has a cross-section of four-leafed clovers. The structure of Th(WO4)(TeO3) exhibits a multilayer-sandwich framework composed of thorium tellurite layers with tungsten chains in between. In the case of the molybdate family, ThMoTe2O9 and Th2(MoO4)(TeO3)3 are built from puckered Th-Te sheets which are further interconnected by MoO4 tetrahedral linkers. The DSC-TG technique was performed to gain insight into the thermal behavior of the synthesized compounds. Raman spectra of as-prepared phases were obtained and analyzed for signature peaks.