Open AccessJournal Article
The crystal chemistry of hexavalent uranium; polyhedron geometries, bond-valence parameters, and polymerization of polyhedra
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The geomeffy, bond valences, and polymerization of hexavalent uranium polyhedra from 105 well-refined structures are analyzed in this article, where a series of coordiaation polyhedr4 from square bipyramidal polyhedras with uranyl ions to holosymmehic octahedral geometry are discussed.Abstract:
The geomeffy, bond valences, and polymerization ofhexavalent uranium polyhedra from 105 well-refined structures are analyzed. The Utu cation is almost always present in crystal stnrctures as part of a nearly linear (UOr)z* uranyl ion that is coordinated by four, five or six equatorial anions in an approximately planar arangement perpendicular to the uranyl ion, giving square, pentagonal and hexagonal bipyramids, respectively. The Utu-O7\" bond length (Oy,: uranyl-ion O atom) is independent of the equatorial anions of the polyhedra;-averages of all polyhedra tlat contain uranyl ions ffs; I6lIJ6f-Or. = 1.79(3), mg0.-.9 a,= 1.79(4), and t8lu6+-Our = 1.78(3) A. Not a[ r6lu6+ polyhedra contain uranyl ions; there is a continuous series of coordiaation polyhedr4 from square bipyramidal polyhedra with uranyl ions to holosymmehic octahedral geometry. The mUo* and t8lu6+ polyhedra invariably contaitl a uranyl ion. The equatorial U6.-0 (0: O,-, OH-) bond-lengths of uranyl polyhedra depend upon coordhation number; averages for all polyhedra are t6lu6+-dq = 2,28(5), rlUot-$* = 2.37(9), afi t8tlJ6+-$q2.47 (12) A. Cunently available bond-valence parameters for U& are unsatisfactory for determining bond-valence sums. Coordination-specific bond-valence paxameters have been derived for U6|, together with parameters applicable to all coordination geometries. The parameters give bond-valence sums for Ue of -6 vlr and reasonable bond-valences for Uc,-Ou, bonds. The bond-valence paraneters facilitate the recognition of Ua, U5+ and U6| catiotrs in refined crystal structures. The crystal-chemical consfraints ofpolyhedral polymerization in uranyl phases are discussed.read more
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U6+ minerals and inorganic compounds: insights into an expanded structural hierarchy of crystal structures
TL;DR: In this article, 368 inorganic crystal structures that contain essential U6+ are considered (of which 89 are minerals) and arranged on the basis of the topological details of their structural units, which are formed by the polymerization of polyhedra containing higher-valence cations.
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Uranium Co-precipitation with Iron Oxide Minerals
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Comprehensive derivation of bond-valence parameters for ion pairs involving oxygen
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Characterization of U(VI)-carbonato ternary complexes on hematite: EXAFS and electrophoretic mobility measurements
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The crystal chemistry of uranium carboxylates
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References
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Journal ArticleDOI
Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides
TL;DR: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations as mentioned in this paper.
Journal ArticleDOI
Bond-valence parameters for solids
N. E. Brese,Michael O'Keeffe +1 more
TL;DR: In this article, it is shown that there is a strong linear correlation between the parameters for bonds from cations to pairs of anions, and this correlation is used to develop an interpolation scheme that allows the estimation of bond-valence parameters for 969 pairs of atoms.
Journal ArticleDOI
Empirical parameters for calculating cation–oxygen bond valences
I. D. Brown,K. K. Wu +1 more