A topologically novel sheet of uranyl pentagonal bipyramids in the structure of Na[(UO2)4O2(OH)5](H2O)2

A new sodium uranyl oxide hydrate, Na[(UO2)(4)O-2(OH)(5)](H2O)(2), has been synthesized by hydrothermal reaction. The structure, space group P (1) over bar, a 8.0746(9), b 8.4633(10), c 11.2181(13) Angstrom, alpha 80.398(2), beta 87.492(2), gamma 71.308(2)degrees, V 715.97(14) Angstrom(3), Z = 2, has been solved and refined on the basis of F-2 for all unique data collected with monochromatic MoKalpha X-radiation and a CCD-based detector to an agreement factor (R1) of 4.49%, calculated using 2915 unique observed reflections (F-O greater than or equal to 4sigma(F)). The structure contains four symmetrically distinct U6+ cations, each of which is strongly bonded to two atoms Of 0, giving (UO2)(2+) uranyl ions. Each uranyl ion is coordinated by five anions. The resulting uranyl pentagonal bipyramids are linked by sharing vertices and edges, resulting in sheets with a previously unobserved topology. The single symmetrically distinct Na cation is located between the sheets, where it is coordinated by eight ligands, including two H2O groups. The structure of Na[(UO2)(4)O-2(OH)(5)](H2O)(2) is closely related to that of Ca[(UO2)(4)O-3(OH)(4)](H2O)(2), although the sheets in these two structures have different topologies.