A Novel Open Framework Uranyl Molybdate: Synthesis and Structure of (NH<sub>4</sub>)<sub>4</sub>[(UO<sub>2</sub>)<sub>5</sub>(MoO<sub>4</sub>)<sub>7</sub>](H<sub>2</sub>O)<sub>5</sub>
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Single crystals of (NH4)4[(UO2)5(MoO4)7](H2O)5 have been synthesized hydrothermally using (NH4)6Mo7O24, (UO2)(CH3COO)2·2H2O, and H2O at 180 °C. The phase has been characterized by single-crystal X-ray diffraction using a merohedrally twinned single crystal: it is hexagonal, P61, a = 11.4067(5) Å, c = 70.659(5) Å, V = 7961.9(7) Å3, and Z = 6. The structure is based upon an open framework with composition [(UO2)5(MoO4)7]4- that is composed of UO7 pentagonal bipyramids that share vertexes with MoO4 tetrahedra. The framework has large channels (effective pore size: 4.8 × 4.8 Å2) parallel to the c axis and a system of smaller channels (effective pore size: 2.5 × 3.6 Å2) parallel to [100], [110], [010], [1̄10], [11̄0], and [1̄1̄0]. The channels are occupied by NH4+ cations and H2O molecules. The topological structure of the uranyl molybdate framework can be described either in terms of fundamental chains of UO7 pentagonal bipyramids and MoO4 tetrahedra or in terms of tubular building units parallel to the c axis.
