High-Temperature, High-Pressure Hydrothermal Synthesis and Characterization of an Open-Framework Uranyl Silicate with Nine-Ring Channels: Cs2UO2Si10O22

A new uranium(VI) silicate, Cs2UO2Si10O22, has been synthesized by a high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction, luminescence, and solid state NMR spectroscopy. It crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 12.2506(4) angstrom, b = 8.0518(3) angstrom, c = 23.3796(8) angstrom, beta = 90.011(2)degrees, and Z = 4. Its structure consists of silicate double layers in the ab plane which are connected by UO6 tetragonal bipyramids via four equatorial oxygen atoms to form a 3D framework with nine-ring channels parallel to the b axis where the Cs+ cations are located. The photoluminescence emission spectrum at room temperature consists of one broad structured band which is typical of uranyl. The Si-29 MAS NMR spectrum is consistent with the crystal structure as determined from X-ray diffraction, and the resonances in the spectrum are assigned. A comparison of related uranyl silicate structures is made.