The crystal structure of Li2Mg2[Si4O11], a loop-branched dreier single chain silicate

Abstract

Abstract The structure of Li2Mg2[Si4O11] was determined by single crystal X-ray diffraction. It is triclinic, space group P[unk], with a = 8.645(1) Å, b = 7.401(1) Å, c = 6.884(1) Å, α = 104.71(1)°, β = 101.08(1)°, γ = 99.41(1)°, V = 407.5(6) Å3 and Z = 2. Least -squares refinements based on 1462 observed reflections with intensities I ≥ 3σ(I) resulted in R = 0.054 and Rw = 0.036. The main structural elements are chains of corner-linked [SiO4] tetrahedra and ribbons consisting of edge-linked [MgO6] octahedra and [LiOn] polyhedra. The [SiO4] tetrahedral chain can be described as a loop-branched dreier single chain. This structure type has not been reported for other silicates. Tetrahedral chains and octahedral ribbons are arranged in layers of tetrahedra and octahedra, respectively, which are alternately stacked parallel to (110) and are linked by shared oxygen atoms. This structural arrangement, known from the structures of pyroxenes, pyroxenoids and amphiboles, is compared in detail with that of the closely related pyroxenoid-like dreier single chain silicates. The topology of the tetrahedral-octahedral linkage which occurs at the apical oxygen atoms of the chains is similar to that in serandite, while the linkage with the basal oxygen atoms of the chains is similar to that in wollastonite. Thus, Li2Mg2[Si4O11] represents a new structural member of the family of the pyroxenoid-like single chain silicates.