Zu Oxoiridaten mit quadratisch-planaren [IrO4]4−-Gruppen: Na4IrO4, eine MgO-Ersetzungsvariante mit geordneten Lücken im Anionenteilgitter

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; R_w = 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 O^2? 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.