Hydrothermal Synthesis, Crystal Structure, and Solid-State NMR Spectroscopy of a New Indium Silicate: K2In(OH)(Si4O10)

A new indium(III) silicate, K2In(OH)(Si4O10), has been synthesized by a high-temperature, high-pressure hydrothermal method. It crystallizes in the monoclinic space group P21/m (No. 11) with a = 11.410(1) (angstrom), b = 8.373(1) (angstrom), c = 11.611(1) (angstrom), (beta) = 112.201(2), and Z = 4. The structure, which is analogous to that of K2CuSi4O10, consists of unbranched vierer 4-fold chains of corner-sharing SiO4 tetrahedra running along the b axis linked together via corner sharing by chains of trans-corner-sharing InO4(OH)2 octahedra to form a 3-D framework which delimits 8-ring and 6ring channels to accommodate K+ cations. The presence of hydroxyl groups is confirmed by IR spectroscopy. The 29Si MAS NMR exhibits four resonances at -88.6, -90.1, -97.4, and -98.2 ppm corresponding to four distinct crystallographic Si sites. A 1H (right arrow) 29Si CP/MAS NMR experiment was performed to assign the four resonances.