Crystal chemistry of uranyl molybdates; I, The structure and formula of umohoite

The structure of umohoite, [(UO (sub 2) )MoO (sub 4) (H (sub 2) O)](H (sub 2) O), triclinic, space group P1, a 6.3748, b 7.5287, c 14.628 Aa, alpha 82.64, beta 85.95, gamma 89.91 degrees , V 694.52 Aa (super 3) , has been solved and refined to R 4.6%. The structure differs from models previously proposed in both the coordination of the cations and the connectivity of the structure. It contains two non-equivalent U sites occupied by U (super 6+) cations, each being part of a nearly linear (UO (sub 2) ) (super 2+) uranyl ion (Ur) that is further coordinated by five O atoms at the equatorial corners of pentagonal bipyramids capped by the O (sub Ur) atoms. Two non-equivalent Mo (super 6+) cations are each coordinated by five O atoms and one H (sub 2) O group; the O atoms are arranged at the apices of a aquare bipyramid, with Mo (super 6+) -O bond-lengths 2.44-2.46 Aa. The cation polyhedra link by sharing edges, forming sheets with the uranophane anion-topology, in which the pentagons are populated by uranyl ions and the squares are populated by Mo (super 6+) . The interlayer at z = 0 contains H (sub 2) O groups, whereas the interlayer at z = 0.5 is not occupied. Sheets are linked by hydrogen bonding, with bonds bridging between sheets where H (sub 2) O is absent, and to H (sub 2) O groups in the interlayer where they are present.