The crystal structure and crystal chemistry of uranosphaerite, Bi(UO (sub 2) )O (sub 2) OH

The crystal structure of uranosphaerite from the Clara baryte and fluorite mine, Black Forest, Germany, was refined to R 2.86 %; a 7.559, b 7.811, c 7.693 Aa, beta 92.88 degrees , V 453.6 Aa (super 3) , space group P2 (sub 1) /n; synthetic uranosphaerite (R 5.84 %) gave a 7.540, b 7.801, c 7.674 Aa, beta 92.948 degrees , V 450.75 Aa (super 3) , The structure consists of one symmetrically distinct U (super 6+) cation bonded to two atoms of oxygen, forming a nearly linear uranyl ion [(UO (sub 2) ) (super 2+) , designated Ur]. The uranyl ion is further coordinated by five O and OH anions, resulting in a pentagonal bipyramid capped by the O of the uranyl ion. The single symmetrically distinct Bi (super 3+) cation is coordinated by four anions arranged at the base of a pyramid that is capped by Bi (super 3+) ; this Bi (super 3+) cation is weakly bonded to two additional O (sub Ur) (sub ) atoms. Urphi (sub 5) (phi = O,OH) pentagonal bipyramids share an equatorial edge, giving a dimer. Pairs of Biphi (sub 4) polyhedra also share an edge, and the resulting dimers are linked to those of the uranyl polyhedra, forming a heteropolyhedral sheet (101). Adjacent sheets are linked by weak Bi--O bonds and by weak hydrogen bonds.