K5(UO2)2[Si4O12(OH)]:: A uranyl silicate containing chains of four silicate tetrahedra linked by SiO•••HOSi hydrogen bonds

A new uranium(VI) silicate, K-5(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) Angstrom, b = 12.2635(7) Angstrom, c = 22.233(1) Angstrom, 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 H-1 MAS NMR spectrum, which is assigned to the (SiOHOSi)-H-... hydrogen bond. A comparison of uranyl silicate structures is made.