Abstract
Six novel uranyl nitrate compounds K3[(UO2)(NO3)Cl3](NO3) (1, 2), α-Cs2[(UO2)(NO3)Cl3] (3), [(UO2)(NO3)2(H2O)2][(CH3NH3)2(NO3)2] (4), Cs2[(UO2)(NO3)4] (5), and [(UO2)2(OH)2(NO3)2(H2O)3](H2O) (6) have been prepared from aqueous solutions. Their structures were analyzed using single-crystal X-ray diffraction technique. Structural studies have shown that the crystals of 1 and 2 are isotypic but differ in the distortion at the counter ion’s sites. The crystal of 3 is a low-temperature polymorph modification of the recently studied compound. The crystal structure of 4 is composed of uranyl-dinitrate-dihydrate and methylamine-nitrate electroneutral complexes linked through the system of H-bonds. The crystal structure of 5 is based on the finite [(UO2)(NO3)4]2− clusters that are arranged in pseudo-chained complexes extended along [100] and are arranged according to a hexagonal packing or rods. The crystal of 6 is also a novel polymorph modification of previously studied compound, the structure of which is based on the very rare topological type of the finite clusters. Nowadays, uranyl nitrate finite clusters of nine various topological types are known. We give herein a short review of their topological features and relationships. Crystallization of uranyl nitrates usually occurs when all other competitive anions in the system have already formed crystalline phases, or the reaction of reagents have slowed down or even stopped. Thus it is suggested that crystallization of uranyl nitrates can be used as a key indicator of the reaction progress, which points to the necessity of the initial concentrations of reagents correction, or to the replacement of reagents and adjustment of the thermodynamic (P,T) parameters of the synthesis.
Highlights
Uranyl nitrate is a very important compound in nuclear wastes management and modern synthetic chemistry of U
Uranyl nitrate is obtained after dissolution of spent nuclear fuel in nitric acid, prior to the preparation of UF6, which is used in uranium enrichment [1,2]
We have reported on the synthesis and characterization of six novel uranyl nitrate phases, in which crystal structures are based on the finite clusters of various topological types
Summary
Uranyl nitrate is a very important compound in nuclear wastes management and modern synthetic chemistry of U. Uranyl nitrate is obtained after dissolution of spent nuclear fuel in nitric acid, prior to the preparation of UF6 , which is used in uranium enrichment [1,2]. The first amounts of plutonium were obtained after irradiation of uranyl nitrate [3]. Uranyl nitrate hexahydrate was used in photographic processes since the 19th century and in the porcelain industry [4], and currently, it is one of the most popular reagents in laboratories to carry out various U-bearing phase formation experiments. There are 108 inorganic and organically templated uranyl nitrate compounds that are listed in the Cambridge Crystallographic Data Centre (CCDC; version 2020.2.0, May 2020 update) and Inorganic Crystal Structure Database (ICSD; version 4.5.0) [5,6]. The majority of them (89) have their structure built on the finite clusters, 16 structures are based on the chained complexes and Crystals 2020, 10, 1122; doi:10.3390/cryst10121122 www.mdpi.com/journal/crystals
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