U (super 6+) minerals and inorganic phases; a comparison and hierarchy of crystal structures

Abstract

AssrRAcr A hierarchical structural classification is developed for Utu minerals and inorganic phases, based on the polymerization of coordination polyhedra of higher bond-valence. The Utu cation is usually present as part of the approximately linear (UfiOr2+ uranyl (Ur) ion, which is coordinated by four, five or six anions (Q: O2-,OH-,H2O), with the oxygen atoms of the uranyl ion forming the apices of square, pentagonal and hexagonal bipyramids, respectively. The uranyl ion bond-lengths are -1.8 A in each coordination polyhedron, and the equatorial bondlengths for U4+ U$s and Ur$6 polyhedra are 2.26(8), 2.34(10) nd 2.46(12) A, respectivd. Inorganic oxide phases in which UG plays a significant sffuctural role are considered. A total of one hundred and eighty structures (of which fifty-six are of minerals) have been placed in the hierarchy of structures: one hundred and six (fony-three minerals) contain infinite sheets of polyhedra, nineteen (five minerals) contain eight different infinite chains of polyhedra, rwenty-two (five minerals) contain ten different finite clusters of polyhedra, seven (no minerals) contain isolated polyhedr4 and twenty-six (three minerals) structures contain frameworks of polyhedra. The sheets of polyhedra that occur in one hundred and six structures are classified according to the details of their topological arrangements of anions within the sheets, with twenty-nine ffierent sheet anion-topologies observed, but six of these topologies account for 827o of observed sheets.