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) Å, b = 8.373(1) Å, c = 11.611(1) Å, β = 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 6-ring 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 → ²⁹Si CP/MAS NMR experiment was performed to assign the four resonances.