X-ray diffraction study of K3NdSi7O17: a new framework silicate with a linear Si-O-Si bond.

Hydrothermal investigations in the high-silica region of the K(2)O-Nd(2)O(3)-SiO(2) system, carried out in a search for novel fast-ion conductors (FICs), yielded the new compound tripotassium neodymium heptasilicate, K(3)NdSi(7)O(17). Single-crystal X-ray methods revealed that K(3)NdSi(7)O(17) crystallizes in space group P3, has lattice constants a = 16.131 (2) and c = 7.7146 (19) A, Z = 4, and 22 atoms in the asymmetric unit. Refinement was carried out to a residual, R(F), of 0.0253 and a weighted residual, wR(F(2)), of 0.0702 using anisotropic displacement parameters for all atoms. The silicate anion forms an interrupted framework, within which both Nd octahedra and K polyhedra are situated. The structure is unusual in that it contains a symmetry-constrained Si-O-Si bond angle of 180 degrees. No isomorphs to K(3)NdSi(7)O(17) are known.