A new uranyl sheet in K5[(UO2)10O8(OH)9](H2O):: New insight into sheet anion-topologies

The structure of K-5[(UO2)(10)O-8(OH)(9)](H2O), Z = 4, monoclinic, space group Pn, a 13.179(2), b 20.895(4), c 13.431(3) Angstrom, beta 106.316(3)degrees, has been solved and refined to R = 7.8% and a goodness-of fit of 0.82 for 4349 unique observed (F-o greater than or equal to 4 sigma(F)) reflections collected for a synthesized crystal using MoK alpha X-radiation and a CCD detector. The structure is dominated by previously unknown sheets of edge- and vertex-sharing uranyl polyhedra parallel to (100), with K cations and H2O groups in the interlayer. The sheets contain 20 symmetrically distinct U6+ cations, each of which is associated with an approximately linear (UO2)(2+) uranyl ion (Ur), and is coordinated by four or five additional anions at the equatorial positions of square (2 polyhedra) and pentagonal (18 polyhedra) bipyramids, respectively. As is the case with other sheets of uranyl polyhedra, the anion topology of the sheet can be generated using a chain-stacking sequence; however, the sequence is unique and for the first time involves the occurrence of P chains flanked by U or D chains of opposite directional sense. This example serves to further demonstrate the structural complexity that is possible in sheets of uranyl polyhedra.