Flux synthesis, crystal structures, and solid-state NMR spectroscopy of two indium silicates containing varied in-O coordination geometries

Two novel indium silicates, K₅In₃Si₇O ₂₁ (1) and K₄In₂Si₈O₂₁ (2), have been synthesized by a flux-growth method and characterized by single-crystal X-ray diffraction. The structure of 1 consists of siebener single chains of corner-sharing SiO₄ tetrahedra running along the b axis linked via corner-sharing by In₂O₉ face-sharing octahedral dimers and InO₅ trigonal bipyramids to form a 3D framework. The structure of 2 consists of a 3D silicate framework containing 6- and 14-ring channels. InO₅ square pyramids are located within the 14-ring channels sharing corners with the silicate framework. The solid-state ²⁹Si MAS NMR spectrum of compound 1 was recorded; it shows the influence of the indium atoms in the second coordination sphere of the silicon on the chemical shift. Crystal data: 1, orthorhombic, Pna2₁ (No. 33), a = 12.4914(3) Å, b = 16.8849(3) Å, c = 10.2275(2) Å, V = 2157.1(1) ų and Z= 4; 2, monoclinic, P2₁/n (No. 14), a = 8.4041(3) Å, b = 11.4919(4) Å, c = 10.4841 (3) Å, β = 90.478(2)°, V = 1012.5(1) ų and Z = 2.