Complex Cobalt Silicates and Germanates Crystallizing in a Porous Three-Dimensional Framework Structure
Four new cesium containing complex cobalt oxides, Cs(Co0.5Si0.5)SiO4 (1), Cs1.29(5)Co0.69(5)Ge1.81(5)O5 (2) and its ordered analogue Cs2CoGe4O10 (3), were synthesized using a mixed CsCl-CsF flux at 850 °C and 900 °C, respectively. The structure of (1) closely resembles that of known zeolite and feldspar structure types and 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)°. Structures (2) and (3) crystallize in the same new structure type, a highly porous three-dimensional framework, in the tetragonal space group I-4 with lattice parameters of a = 7.4239(14) Å and c = 13.169(3) Å and a = 7.3540(6) Å and c = 13.1122(11) Å, respectively. The formation of (2) vs (3) can be targeted by using slight variations in the quantities of starting materials. Single crystal to single crystal ion exchange experiment on (1) carried out in a molten RbNO3 bath results in 14% Cs exchange with Rb, affording the composition, Cs0.86Rb0.14(Co0.5Si0.5)SiO4 (4). First-principles calculations in the form of density functional theory (DFT) were performed for (1) and (3) to elucidate their electronic and magnetic properties, and stability at 0 K.