Abstract: | Preparation of Crystal Structure of K6Al2O6] and Rb6Al2O6] Colourless single crystals of K6Al2O6] have been prepared from intimate mixtures of KAlO2 and K2O (550°C, 90 d). The structure determination from four-circle diffractometer data (MoKα , 742 Io(hkl), R = 2.2%, Rw = 2.1%) confirms the space group C2/m with Z = 2; a = 698.25 pm, b = 1 103.54 pm, c = 646.49 pm, β = 102.49°. Colourless single crystals of hitherto unknown Rb6Al2O6] have been prepared from intimate mixtures of RbAlO2 and Rb2O (520°C, 120 d). The structure determination from four-circle diffractometer data (MoKα , 1 240 Io(hkl)) results in the residual values R = 7.2%, Rw = 4.9%; space group C2/m; a = 725.92 pm, b = 1 143.33 pm, c = 678.06 pm, β = 104.05°; Z = 2. K6Al2O6] and Rb6Al2O6] are isostructural with K6Fe2O6]. A characteristic structure unit is the anion Al2O6]6? consisting of two edge-sharing AlO4] tetrahedra. Effective Coordination Numbers (ECoN), Mean Fictive Ionic Radii (MEFIR), the Madelung Part of Lattice Energy (MAPLE) and the Charge Distribution (CHARDI) are calculated and discussed. |