Abstract
Comparison of the natural and synthetic phases allows an overview to be made and even an understanding of the crystal growth processes and mechanisms of the particular crystal structure formation. Thus, in this work, we review the crystal chemistry of the family of uranyl selenite compounds, paying special attention to the pathways of synthesis and topological analysis of the known crystal structures. Comparison of the isotypic natural and synthetic uranyl-bearing compounds suggests that uranyl selenite mineral formation requires heating, which most likely can be attributed to the radioactive decay. Structural complexity studies revealed that the majority of synthetic compounds have the topological symmetry of uranyl selenite building blocks equal to the structural symmetry, which means that the highest symmetry of uranyl complexes is preserved regardless of the interstitial filling of the structures. Whereas the real symmetry of U-Se complexes in the structures of minerals is lower than their topological symmetry, which means that interstitial cations and H2O molecules significantly affect the structural architecture of natural compounds. At the same time, structural complexity parameters for the whole structure are usually higher for the minerals than those for the synthetic compounds of a similar or close organization, which probably indicates the preferred existence of such natural-born architectures. In addition, the reexamination of the crystal structures of two uranyl selenite minerals guilleminite and demesmaekerite is reported. As a result of the single crystal X-ray diffraction analysis of demesmaekerite, Pb2Cu5[(UO2)2(SeO3)6(OH)6](H2O)2, the H atoms positions belonging to the interstitial H2O molecules were assigned. The refinement of the guilleminite crystal structure allowed the determination of an additional site arranged within the void of the interlayer space and occupied by an H2O molecule, which suggests the formula of guilleminite to be written as Ba[(UO2)3(SeO3)2O2](H2O)4 instead of Ba[(UO2)3(SeO3)2O2](H2O)3.
Highlights
All natural compounds of U(VI) and selenium are selenites
Guilleminite, Ba[(UO2 )3 (SeO3 )2 O2 ](H2 O)3 [1,27], and demesmaekerite, Pb2 Cu5 [(UO2 )2 (SeO3 )6 (OH)6 ](H2 O)2 [2,28], were the first uranyl selenites found in nature (Table 1)
The first mineral was named after the general director of the Union Minière du Haut-Katanga (UMHK), co-founder of the International Mineralogical Association, French chemist and mineralogist, Jean-Claude Guillemin
Summary
All natural compounds of U(VI) and selenium are selenites. Uranyl selenites can be justifiably attributed to rare mineral species. Crystals 2019, 9, 639 demesmaekerite, Pb2 Cu5 [(UO2 ) (SeO3 ) (OH)6 ](H2 O)2 [2], marthozite, Cu[(UO2 ) (SeO3 ) O2 ](H2 O)8 [3], derriksite, Cu4 [(UO2 )(SeO3 )2 ](OH)6 [4], haynesite, [(UO2 ) (SeO3 ) (OH)2 ](H2 O)5 [5], piretite, Ca(UO2 ) (SeO3 ) (OH)4 ·4H2 O [6], and larisaite, Na(H3 O)[(UO2 ) (SeO3 ) O2 ](H2 O)4 [7]. Their occurrence is limited to just a few localities. Apart from mineralogy, uranyl selenites are of great interest from the geochemical and radiochemical points of view
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
