The crystal structure of aklimaite, Ca₄[Si₂O₅(OH)₂](OH)₄· 5 H₂O

Abstract

Aklimaite, Ca4[Si2O5(OH)2](OH)4 · 5 H2O, is monoclinic, space group C2/m, a = 16.907(5), b = 3.6528(8), c = 13.068(4) Å, β = 117.25(4)°, V = 717.5(4) Å3, Z = 2. The crystal structure was solved by direct methods and refined to R(F) = 0.1100 for 1196 unique reflections with I > 2σ(I). Aklimaite is a sorosilicate of a new structure type. The structure is based on corrugated layers of Ca-centered polyhedra formed by alternating columns of edge-sharing Ca octahedra and seven-coordinated polyhedra, extending along [010] which are connected with Ca seven-coordinated polyhedra of another type via common edges. Si-centered tetrahedra form isolated Si2O5(OH)2 groups which are combined in a motif like interrupted chains (“dotted lines”) sharing O—O edges with Ca polyhedra of the layers.