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

Abstract

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)Te^IV₆O₁₄], 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)Te^IV₆O₁₄] 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.