AUTHOR=Hao Yucheng , Langer Eike M. , Xiao Bin , Kegler Philip , Cao Xin , Hu Kunhong , Eichel Rüdiger-A. , Wang Shuao , Alekseev Evgeny V. 

TITLE=Understanding of the structural chemistry in the uranium oxo-tellurium system under HT/HP conditions

JOURNAL=Frontiers in Chemistry

VOLUME=11

YEAR=2023

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2023.1152113

DOI=10.3389/fchem.2023.1152113

ISSN=2296-2646

ABSTRACT=<p>The study of phase formation in the U-Te-O systems with mono and divalent cations under high-temperature high-pressure (HT/HP) conditions has resulted in four new inorganic compounds: K<sub>2</sub> [(UO<sub>2</sub>) (Te<sub>2</sub>O<sub>7</sub>)], Mg [(UO<sub>2</sub>) (TeO<sub>3</sub>)<sub>2</sub>], Sr [(UO<sub>2</sub>) (TeO<sub>3</sub>)<sub>2</sub>] and Sr [(UO<sub>2</sub>) (TeO<sub>5</sub>)]. Tellurium occurs as Te<sup>IV</sup>, Te<sup>V</sup>, and Te<sup>VI</sup> in these phases which demonstrate the high chemical flexibility of the system. Uranium VI) adopts a variety of coordinations, namely, UO<sub>6</sub> in K<sub>2</sub> [(UO<sub>2</sub>) (Te<sub>2</sub>O<sub>7</sub>), UO<sub>7</sub> in Mg [(UO<sub>2</sub>) (TeO<sub>3</sub>)<sub>2</sub>] and Sr [(UO<sub>2</sub>) (TeO<sub>3</sub>)<sub>2</sub>], and UO<sub>8</sub> in Sr [(UO<sub>2</sub>) (TeO<sub>5</sub>)]. The structure of K<sub>2</sub> [(UO<sub>2</sub>) (Te<sub>2</sub>O<sub>7</sub>)] is featured with one dimensional (1D) [Te<sub>2</sub>O<sub>7</sub>]<sup>4-</sup> chains along the <italic>c</italic>-axis. The Te<sub>2</sub>O<sub>7</sub> chains are further linked by UO<sub>6</sub> polyhedra, forming the 3D [(UO<sub>2</sub>) (Te<sub>2</sub>O<sub>7</sub>)]<sup>2-</sup> anionic frameworks. In Mg [(UO<sub>2</sub>) (TeO<sub>3</sub>)<sub>2</sub>], TeO<sub>4</sub> disphenoids share common corners with each other resulting in infinite 1D chains of [(TeO<sub>3</sub>)<sub>2</sub>]<sup>4-</sup> propagating along the <italic>a</italic>-axis. These chains link the uranyl bipyramids by edge sharing along two edges of the disphenoids, resulting in the 2D layered structure of [(UO<sub>2</sub>) (Te<sub>2</sub>O<sub>6</sub>)]<sup>2-</sup>. The structure of Sr [(UO<sub>2</sub>) (TeO<sub>3</sub>)<sub>2</sub>] is based on 1D chains of [(UO<sub>2</sub>) (TeO<sub>3</sub>)<sub>2</sub>]<sub>∞</sub><sup>2−</sup> propagating into the <italic>c</italic>-axis. These chains are formed by edge-sharing uranyl bipyramids which are additionally fused together by two TeO<sub>4</sub> disphenoids, which also share two edges. The 3D framework structure of Sr [(UO<sub>2</sub>) (TeO<sub>5</sub>)] is composed of 1D [TeO<sub>5</sub>]<sup>4−</sup> chains sharing edges with UO<sub>7</sub> bipyramids. Three tunnels based on 6-Membered rings (MRs) are propagating along [001] [010] and [100] directions. The HT/HP synthetic conditions for the preparation of single crystalline samples and their structural aspects are discussed in this work.</p>