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

Abstract

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: K₂ [(UO₂) (Te₂O₇)], Mg [(UO₂) (TeO₃)₂], Sr [(UO₂) (TeO₃)₂] and Sr [(UO₂) (TeO₅)]. Tellurium occurs as Te^IV, Te^V, and Te^VI in these phases which demonstrate the high chemical flexibility of the system. Uranium VI) adopts a variety of coordinations, namely, UO₆ in K₂ [(UO₂) (Te₂O₇), UO₇ in Mg [(UO₂) (TeO₃)₂] and Sr [(UO₂) (TeO₃)₂], and UO₈ in Sr [(UO₂) (TeO₅)]. The structure of K₂ [(UO₂) (Te₂O₇)] is featured with one dimensional (1D) [Te₂O₇]^4- chains along the c-axis. The Te₂O₇ chains are further linked by UO₆ polyhedra, forming the 3D [(UO₂) (Te₂O₇)]^2- anionic frameworks. In Mg [(UO₂) (TeO₃)₂], TeO₄ disphenoids share common corners with each other resulting in infinite 1D chains of [(TeO₃)₂]^4- propagating along the a-axis. These chains link the uranyl bipyramids by edge sharing along two edges of the disphenoids, resulting in the 2D layered structure of [(UO₂) (Te₂O₆)]^2-. The structure of Sr [(UO₂) (TeO₃)₂] is based on 1D chains of [(UO₂) (TeO₃)₂]_∞ ^2- propagating into the c-axis. These chains are formed by edge-sharing uranyl bipyramids which are additionally fused together by two TeO₄ disphenoids, which also share two edges. The 3D framework structure of Sr [(UO₂) (TeO₅)] is composed of 1D [TeO₅]^4- chains sharing edges with UO₇ 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.

Keywords: crystal structure; crystals; highpressure; hightemperature; tellurium; uranium.