Crystal structures of the solid solutions Na₃Zn_0.912Cd_0.088B₅O₁₀ and Na₃Zn_0.845Mg_0.155B₅O₁₀

Two new penta-borates, tris-odium zinc cadmium penta-borate, Na₃Zn_0.912Cd_0.088B₅O₁₀, and tris-odium zinc magnesium penta-borate, Na₃Zn_0.845Mg_0.155B₅O₁₀, have been synthesized by high-temperature solution reactions at 1023 K. Their crystal structures were determined by single-crystal X-ray diffraction. Both solid solutions crystallize in the ortho-rhom-bic form of the parent compound Na₃ZnB₅O₁₀ (space group type Pbca, Z = 8) and contain the double ring [B₅O₁₀]^5- anion composed of one BO₄ tetra-hedron and four BO₃ triangles as the basic structural motif. The anions are bridged by tetra-hedrally coordinated and occupationally disordered M²⁺ (M = Zn/Cd, Zn/Mg) cations via common O atoms to form [MB₅O₁₀] ³ layers. The intra-layer inter-secting channels and the inter-layer voids are occupied by Na⁺ cations to balance the charge.