The First Sodium Uranyl Chromate, Na₄[(UO₂)(CrO₄)₃]: Synthesis and Crystal Structure Determination

Abstract

The first sodium uranyl chromate, Na 4 [(UO 2 )(CrO 4 ) 3 ], has been obtained by high-temperature solid-state reaction. The structure (triclinic, P1, Z ϭ 2, a ϭ 7.1548(3), b ϭ 8.4420(3), c ϭ 11.5102(5) Å , α ϭ 80.203(1)°, β ϭ 79.310(1)°, γ ϭ 70.415(1)°V ϭ 639.24(4) Å 3 ) has been solved by direct methods and refined on the basis of F 2 for all unique reflections to R1 ϭ 0.024 [calculated on the basis of 4374 unique observed reflections (ΗF o Η Ն 4σ F )]. The structure is based on chains of composition [(UO 2 )(CrO 4 ) 3 ] that are parallel to [101]. The chains contain UrO 5 pentagonal bipyra-

Crystal Chemistry and Structural Complexity of Natural and Synthetic Uranyl Selenites

“…However, synthetic uranyl selenite 9 was grown at slightly higher temperatures of 80 • C. Moreover, the presence of rather specific uranyl tetragonal bipyramids in the structure of derriksite refers to a family of isotypic uranyl phosphate [88], molybdate [89], and tellurite [90] compounds, which were obtained during hydrothermal (above 180 • C) or high temperature solid state (above 650 • C) syntheses. Analogously, the crystal structures of synthetic uranyl chromates [67,68] and molybdates [69], which are isotypic to that one of demesmaekerite, were obtained at hydrothermal conditions (above 120 • C) or solid state reactions (at 300 • C). Nevertheless, based on laboratory [91,92] and field observations, namely of the mineral association from Zálesí (Czech Republic) [8], it is clear that demesmaekerite and piretite (and several other unnamed or poorly identified U-Se phases) formed as a result of supergene alteration processes, which exclude hydrothermal activity.…”

Uncovering the Origin of Divergence in the CsM(CrO4)2 (M = La, Pr, Nd, Sm, Eu; Am) Family through Examination of the Chemical Bonding in a Molecular Cluster and by Band Structure Analysis

“…59 Th IV and U VI chromates have been the subject of numerous investigations and show a vast array of structural topologies. [60][61][62][63][64][65][66] However, both of these actinide cations are 5f 0 , and therefore lack many of the interesting electronic characteristics found in later actinide compounds.…”

“…Complicating matters further, chromates also form undesirable inclusions in the form of spinels during vitrification of nuclear waste . Th IV and U VI chromates have been the subject of numerous investigations and show a vast array of structural topologies. − However, both of these actinide cations are 5f 0 and therefore lack many of the interesting electronic characteristics found in later actinide compounds.…”

22 New compounds and structures in the solid state

“…The chains are linked by Na 1 cations. 75 The structures of RE(MoO 2 )(IO 3 ) 4 (OH) [RE ~Nd, Sm, Eu] have threedimensional networks composed of eight-coordinate square antiprismatic RE 31 cations and MoO 2 (OH) 1 moieties that are bound together by distorted bridging iodate anions. The Mo(VI) atoms are thus in distorted octahedral environments composed of two cis-oxo atoms, a hydroxo group and three bridging iodate anions arranged in a fac geometry.…”