Ein neues Oxoberyllat: K2Na4[O2BeOBeO2]

On K₂Na₄O₂BeOBeO₂] For the first time colourless single crystals of K₂Na₄Be₂O₅] which are isotypic with K₂Na₄Co₂O₅] 2] and Rb₂Na₄Co₂O₅] have been prepared by heating e.g. a well ground mixture of K₂O, Na₂O and BeO (K:Na:Be = 2.2:4.4:2; 750°C; 21 d; Ni-tube). The crystal structure was solved by four-circle diffractometer data Siemens AED 2; 389 I_o(hkl); space group P4₂/mnm; Z = 2; a = 595.17(4) pm, c = 1 002.66(9) pm; R = 4.1%; R_w = 2.3%]. Mean Fictive Ionic Radii, MEFIR, Effective Coordination Numbers, ECoN, the Madelung Part of Lattice Energy, MAPLE, and the charge distribution are calculated.