Crystal chemistry of uranyl molybdates.: III.: New structural themes in Na6[(UO2)2O(MoO4)4] Na6[(UO2)(MoO4)4] and K6[(UO2)2O(MoO4)4]

Two Na uranyl molybdates, Na-6[(UO2)(2)O(MoO4)(4)] and Na-6[L(UO2)(MoO4)(4)]: and one K uranyl molybdate, K-6[(UO2)(2)O(MoO4)(4)] have been synthesized by high-temperature solid-state reactions of mixtures of Na2CO3, K2CO3, Uo(3) and MoO3. All three structures were solved by direct methods and refined on the basis of F-2 for all unique data collected with monochromatic MoK alpha X-radiation and a CCD (charge-coupled device) detector. The structure of Na-6[(UO2)(2)O(MoO4)(4)] was refined to an agreement factor (R1) of 4.1%, calculated using the 1969 unique observed reflections (F-o greater than or equal to 4 sigma (F)), and a goodness-of-fit (S) of 1.06. It is triclinic, space group P (1) over bar, a 7.637(2), b 8.164(2), c 8.746(1) Angstrom, alpha 72.329(5), beta 79.364(5), gamma 65.795(4)degrees V472.7(2) Angstrom (3), Z = 1 The structure of Na-6[(UO2)(MoO4)(4)] was refined to an R1 of 3.3%, calculated using the 3268 unique observed reflections (Fo greater than or equal to 4 sigma (F)), and a S of 0.97. It is triclinic, space group P (1) over bar, a 7.0958(8), b 9.566(1), c 13.415(2) Angstrom, alpha 73.692(2), beta 86.621(2), gamma 82.940(2)degrees, V 867.0(2) Angstrom (3), Z = 2. The structure of K-6[(UO2)(2)O(MoO4)(4)] was refined to an R1 Index of 4.9%, calculated using the 1833 unique observed reflections (F-o > 4 sigma (F)). and a S of 0.90. It is triclinic, space group P (1) over bar, a 7.8282(8), b 7.8298(8), c 10.302(1) Angstrom, alpha 83.893(2), beta 73.13(2), gamma 80.338(2)degrees, V 594.6(1) Angstrom (3), Z = 1 The structural connectivity of these three compounds is notable in that each exhibits themes nor previously observed in uranyl compounds. The structures of both Na-6[(UO2)(2)O(MoO4)(4)] and K-6[(UO2)(2)O(MoO4)(4)] contain chains of polyhedra of composition [(UO2)(2)O(MoO4)(4)](6-). These chains have not been previously observed and are composed of [UrO(4)OUrO(4)] dimers consisting of two UrO(5) (Ur: uranyl ion) pentagonal bipyramids sharing a common O atom. The dimers are connected into a chain by sharing vertices with MoO4 tetrahedra with the chains linked by Na+ or K+ cations. The structure of Na-6[(UO2)(MoO4)(4)] consists of finite clusters of composition [(UO2)(2)(MoO4)(8)](12-) composed of two UrO(5) pentagonal bipyramids connected by sharing vertices with MoO4 tetrahedra. The clusters in Na-6[(UO2)(MoO4)(4)] are oriented parallel to the (001) plane and are linked through Na+ cations.