Complex cobalt silicates and germanates crystallizing in a porous three-dimensional framework structure

Abstract

Four new cesium-containing cobalt oxide complexes were reported. Cs(Co_0.5Si_0.5)SiO₄ (1), Cs_1.29(5)Co_0.69(5)Ge_1.81(5)O₅ (2), and its ordered analogue Cs₂CoGe₄O₁₀ (3) were synthesized using a mixed CsCl–CsF flux at 850 °C or 900 °C. The structure of (1) closely resembles that of known zeolite and feldspar structures, and (1) crystallizes in the noncentrosymmetric monoclinic space group Im with lattice parameters of a = 8.9926(4) Å, b = 5.4599(2) Å, c = 9.3958(6) Å, and β = 91.5928(18)°. Complexes (2) and (3) crystallize in the same new structure with a highly porous three-dimensional framework in the tetragonal space group I with lattice parameters of a = 7.4239(14) Å and c = 13.169(3) Å for (2) and a = 7.3540(6) Å and c = 13.1122(11) Å for (3). The formation of (2) vs. (3) can be controlled based on slight variations in the quantities of the starting materials. Single-crystal-to-single-crystal ion exchange of (1) in a molten RbNO₃ bath resulted in 14% Cs exchange with Rb, affording the composition Cs_0.86Rb_0.14(Co_0.5Si_0.5)SiO₄ (4). First-principles density functional theory calculations were performed to elucidate the electronic and magnetic properties and stabilities of (1) and (3) at 0 K.