Crystal Structure of B-Type Tm2Si2O7 (≡Tm4[Si3O10][SiO4])

Abstract

Single crystals of B-type thulium oxodisilicate Tm2Si2O7 were obtained by the reaction of Tm, S and RbCl with the wall of a silica tube in an attempt to synthesize ternary alkalimetal thulium sulfides (e.g. Rb3Tm7S12). It crystallizes triclinically in space group P1̄(a = 655.91(5), b = 659.04(5), c = 1195.32(9) pm, α = 94.361(8), β = 91.102(8), γ = 92.005(8)◦), with four formula units of Tm2Si2O7 per unit cell. Instead of pyro-anionic [Si2O7]6− groups the title compound contains both ortho-silicate tetrahedra [SiO4]4− and catena-trisilicate units [Si3O10]8−. Therefore the formula Tm4[Si3O10][SiO4] (Z = 2) appears more adequate. The four crystallographically independent Tm3+ cations show coordination numbers from six to eight with distorted octahedral, bicapped trigonal prismatic and square antiprismatic oxygen coordination spheres.