K<sub>5</sub>(UO<sub>2</sub>)<sub>2</sub>[Si<sub>4</sub>O<sub>12</sub>(OH)]: A Uranyl Silicate Containing Chains of Four Silicate Tetrahedra Linked by SiO···HOSi Hydrogen Bonds
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A new uranium(VI) silicate, K5(UO2)2[Si4O12(OH)], has been synthesized by a high-temperature, high-pressure hydrothermal method. It crystallizes in the orthorhombic space group Pbcm (No. 57) with a = 13.1274(7) Å, b = 12.2635(7) Å, c = 22.233(1) Å, and Z = 8. Its structure consists of unbranched chains of four silicate tetrahedra extending along the b axis linked together via corner-sharing by UO6 tetragonal bipyramids to form a 3-D framework, which delimits intersecting channels along the c and b axes to accommodate K+ cations. A hydrogen atom is bonded to a terminal oxygen of a terminal silicate in the oligosilicate anion. Adjacent chains are linked along the b axis by hydrogen bonds. The sample shows a resonance at 14.7 ppm in the 1H MAS NMR spectrum, which is assigned to the SiO···HOSi hydrogen bond. A comparison of uranyl silicate structures is made.
