Abstract: | On Oxoiridates(IV) with Square-planar Groups IrO4]4?: Na4IrO4, a Substitution-variant of MgO with Ordered Vacancies in the Anionic Part of Structure . For the first time we prepared transparent red single crystals of Na4IrO4] by an “exchange reaction” (Li2IrO3 + 2.20 Na2O; Ag, 800°C, 71 days): tetragonal, space group I4/m (No. 87), a = 716.70(4) pm and c = 471.32(4) pm; Z = 2. The structure determination via four circle diffractometer data (Mo? Kα , graphite; 2 138 I0(hkl), R = 0.0179; Rw = 0.0184) was carried out with all 296 independent reflexions. Therefore Na4IrO4 crystallizes in a defect-variant of MgO which can be derived from Na4UO5. Ir4+ is surrounded square-like by four O2? with two vacancies completing the octahedron. The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated and discussed. Furthermore the mean value for MAPLE(“IrO2”) of all alkaline- and alkaline-earth-oxoiridates(IV) is given. |