The crystal structure of becquerelite from Shinkolobwe (Zaïre) has been determined by X-ray diffraction. Formula : Ca[(UO₂)₆O₄(OH)₆] • 8 H₂O. Orthorhombic system ; space group Pn2₁a ; a = 13.86(2), b = 12.30(1) et c = 14.92(3) Å ; Z = 4. The structure consists of [(UO₂)₆O₄(OH)₆][n times, charged 2n⁻] layers connected by Ca(H₂O)₄ groups and by water molecules. In the layers eachUO₂⁺⁺ is surrounded by 5 oxygen atoms (3 OH⁻⁻ and 2 O⁻⁻) each one shared between 3 U. Ca⁺⁺ is eightfold coordinated (~ square antiprism). The same layers are present in billietite and compreignacite.
The structure o f bromo-5 tetraphenyl-l,2,3,4 cyclopentadiene has been determined byX-rayanalysis.Spacegroup:P2,2,2,,Z = 4 ; a = 8.51,b = 4 1 . 9 9 ,~ = 6.17A. The molecule has nearly mirror-symmetry. The angles between the mean planes of the phenyls and that of the central ring are ~ ( 1 ) = 30.5', ~( 2 ) = 66..5", ~( 3 ) = -69.0" and ~( 4 ) = -33.9'.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.