Crystal structures of Ca5Ge3O11 and wollastonite-type GaGeO3

Abstract

Abstract The crystal structures of triclinic Ca5Ge3O11 and triclinic wollastonite-type CaGeO3 have been determined by X-ray diffraction using single crystals grown from a K2MoO4 flux. Ca5Ge3O11 is closely related to monoclinic Ca5(Ge,Si)3O11 and crystallizes in the C[unk] space group with the cell parameters: a = 10.855(2) Å, b = 8.715(2) Å, c = 10.998(2) Å, α = 90.60(3)°, β = 96.49(3)°, γ = 90.17(3)°, Z = 4, wR(F 2) = 0.080 for 4877 unique reflections. Ca5Ge3O11 is a mixed-anion germanate containing single and double tetrahedra, with a structural formula written as Ca5[GeO4] [Ge2O7]. CaGeO3 is isostructural with CaSiO3, wollastonite-1T, and crystallizes in the P[unk] space group with the cell parameters: a = 7.269(2) Å, b = 7.526(2) Å, c = 8.094(2) Å, α = 103.44(3)°, β = 94.42(3)°, γ = 90.11(3)°, Z = 6, wR(F 2) = 0.074 for 9279 unique reflections. The CaGeO3 structure contains tetrahedral dreier single chains corresponding to the structural formula Ca3{uB∞ 1}[Ge3O9]. The bonding in the two compounds is analyzed in terms of a comparison between observed bond valences and bond valences predicted from the bond topology.