Flux Synthesis, Crystal Structures, and Solid-State NMR Spectroscopy of Two Indium Silicates Containing Varied In−O Coordination Geometries

Two novel indium silicates, K5In3Si7O21 (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) Å3 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) Å3 and Z = 2.