Ca10Ge16B6O51 and Cd12Ge17B8O58: Two Types of New 3D Frameworks Based on BO4 Tetrahedra and 1D [Ge4O12]n Chains

Two new acentric borogermanates, Ca10Ge16B6O51 (Pba2) and Cd12Ge17B8O58 (P4̅), have been successfully synthesized by high-temperature solid-state reactions of CaCO3 (or CdCO3), GeO2, and H3BO3. Both structures display the same one-dimensional (1D) [Ge4O12]n chains composed of GeO4 tetrahedra and GeO6 octahedra. In Ca10Ge16B6O51, neighboring 1D [Ge4O12]n chains are condensed into a two-dimensional (2D) [Ge4O10.75]n layer via corner sharing, and such layers are further interconnected by “isolated” BO4 tetrahedra and B2O7 dimers into a three-dimensional (3D) framework, forming 1D tunnels of 5-, 6-, and 7-MRs along the c axis that are occupied by Ca2+ cations. In Cd12Ge17B8O58, neighboring 1D [Ge4O12]n chains are interconnected into a [Ge4O10.5]n open framework via corner sharing with large pores filled by big [Ge(B2O7)4]28– clusters, leading to formation of three types of 1D tunnels of 5-, 6-, and 7-membered rings (MRs) along the c axis which are occupied by the Cd2+ cations. Both compounds are transparent in the range of 0.3–6.67 μm and exhibit very weak SHG responses.