Unusual Uranyl Tellurites Containing [Te2O6]4 Ions and Three-Dimensional Networks

Abstract

Solid-state chemistry of the actinides is the subject of significant investigation because of its relevance to nuclear waste disposal and power generation, [1] mineralogy, [2] and catalysis. [3] One system that is poorly understood is that of the uranyl tellurites, which are currently known only from three minerals, UO 2 (Te 3 O 7 ), [4] PbUO 2 (TeO 3 ) 2 , [5] and UO 2 (TeO 3 ), [6] and the synthetic phase Pb 2 UO 2 (TeO 3 ) 3 . [7] In spite of their low representation, these compounds differ substantially in their dimensionality, [2] the coordination environments of the U VI center, and in the Te IV oxoanions present.The ubiquitous presence of a stereochemically active lone pair of electrons on the Te IV centers certainly plays a substantial role in the crystalline architecture of this family of compounds. However, the general tendency is for oxoanions containing nonbonding electrons to either not affect the overall dimensionality of U VI compounds, or to reduce it from two-dimensional to one-dimensional, as demonstrated by uranyl iodates [8, 9] and selenites. [10] In uranyl tellurites this trend is not observed. The ability of Te IV to bind four or five O atoms in its inner sphere, as found in the ternary phases, BaTe 3 O 7 , [11] BaTe 4 O 9 , [11] TeSeO 4 , [12] UO 2 (TeO 3 ), [6] and UO 2 (-Te 3 O 7 ) [4] does not offer a satisfying explanation for the atypical behavior of uranyl tellurites because Pb 2 UO 2 (TeO 3 ) 3 contains only TeO 3 2À ions, and yet it still adopts a threedimensional architecture. [7] To address the unusual bonding in the uranyl tellurite system we are systematically preparing a series of compounds by hydrothermal methods that differ primarily in their countercations. For example, the reaction of TlCl with UO 2 (C 2 H 3 O 2 ) 2 ¥2 H 2 O and Na 2 TeO 3 at 180 8C in aqueous media for three days produces Tl 2 [UO 2 (TeO 3 ) 2 ] (1), whereas, in the absence of TlCl, Na 8 [(UO 2 ) 6 (TeO 3 ) 10 ] (2) is isolated instead.The simplicity of the formula of 1 is quite misleading because its structure is far from predictable. The uranyl tellurite architecture in this compound is constructed from uranyl moieties that are bound by five O atoms to create UO 7 pentagonal bipyramids. These polyhedra edge-share to form dimers. The dimers are joined by bridging TeO 3 2À ions to yield one-dimensional chains. The chains are in turn linked by [Te 2 O 6 ] 4À ions that are bischelating/bridging, producing twodimensional 2 1 [UO 2 (TeO 3 ) 2 ] 2À sheets that are separated by Tl þ ions. Part of a 2 1 [UO 2 (TeO 3 ) 2 ] 2À sheet is illustrated in Figure 1. Bond valence sum calculations are consistent with U VI and COMMUNICATIONS 3426

Hydrothermal syntheses and structures of the uranyl tellurates AgUO2(HTeO5) and Pb2UO2(TeO6)

“…These rare minerals are from the oxidizied zone of a U deposit at Shinkolobwe, Democratic Republic of Congo, and the oxidized zone of a hydrothermal Au/Te deposit at the Moctezuma mine in Mexico [4]. More recently, 11 hydrothermally synthesized uranyl tellurites have been synthesized and structurally characterized: Pb 2 UO 2 (TeO 3 ) 3 [5] [6], Na 8 [(UO 2 ) 6 (TeO 3 ) 10 ] [7], A 2 [(UO 2 ) 3 (TeO 3 ) 2 O 2 ] (A¼K, Rb, Cs) [8], and K 4 [(UO 2 ) 5 (TeO 3 ) 2 O 5 ] [9]. Considerable structural diversity is exhibited by these compounds, which contain structural units consisting of uranyl tellurite chains, sheets, and frameworks.…”

New Crystal Structures of Rare‐Earth Metal(III) Oxotellurates(IV) RE2Te3O9: A1‐Type (RE=La, Ce) and A2‐Type (RE=Pr, Nd)

“…This is mainly due to the variability in the coordination environments of the oxotellurate(IV) anion [7–9] and also the presence of a stereochemically active lone‐pair of electrons at their Te 4+ centers. These lone pairs can serve as an invisible structure‐directing ligands, [10–12] which often lead to non‐centrosymmetric structures (NCS) with interesting physical properties, such as non‐linear optical second harmonic generation (SHG), piezo‐, pyro‐ and ferroelectricity [13–17] . When compared to the related oxosulfates(IV), oxoarsenates(III) and oxoselenates(IV) with third and fourth period members of the periodic system of the elements (PSE), which also contain lone‐pair electrons in their ψ 1 ‐tetrahedral [SO 3 ] 2− , [AsO 3 ] 3− and [SeO 3 ] 2− anions, oxotellurates(IV) groups exhibit strong Te 4+ ⋅⋅⋅O 2− secondary bonding interactions (SBIs) between the analogous [TeO 3 ] 2− anions and thus show much better thermal and chemical stabilities.…”

Thorium Chemistry in Oxo-Tellurium System under Extreme Conditions

“…27 Compounds in the second group are derived from the hydrothermal method at relatively low temperature (around 200 °C). Compared to the first group, compounds under hydrothermal condition exhibit more diverse structural architectures, which can be exemplified from the 1D chains observed in β-Tl 2 (UO 2 )(TeO 3 ) 2 28 to the 3D framework found in Na 8 (UO 2 ) 6 (TeO 3 ) 10 . 29 The third group is isolated from the recently developed high-temperature/high-pressure technique.…”