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 P21/c (No. 14) with a = 12.2506(4) Å, b = 8.0518(3) Å, c = 23.3796(8) Å, β = 90.011(2)°, 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 29Si 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.