Ein neuer Strukturtyp bei Oxoiridaten mit quadratisch-planaren [IrO4]4−-Gruppen: K2Na2[IrO4], ein Raumnetz [Na2IrO4] mit Kanälen. (Mit einer Anmerkung zu Rb2Na2[IrO4])

A New Type of Structure in Oxoiridates with Square-planar Groups IrO₄]^4?: K₂Na₂IrO₄], a Network Na₂IrO₄] with Channels (With a Remark on Rb₂Na₂IrO₄]) For the first time magnificent dark red cuboid single crystals of K₂Na₂IrO₄] were prepared by annealing intimate mixtures of a) KO_0.51, Na₂O₂, IrO₂ and Ir-powder (molar proportions 3.02 : 1.40 : 1.00 : 1.00; Ag-bomb, 740°C, 54 d) and of b) KO_0.51, Na₂O and IrO₂ (molar proportions K : Na : Ir = 2.20 : 2.20 : 1.00; Ag-bomb, 760°C, 57 d) respectively. The oxide crystallizes mP36, space group P2₁/c with a = 600.35(6) pm, b = 1111.2(1) pm, c = 933.0(1) pm and β = 113.14(1)°. Structure determination via four-circle diffractometer data (Siemens AED 2, Mo-Kα-Radiation) for all 2347 unique reflexions (merged from 9397 I_o(hkl) gave R = 0.0357 and R_w = 0.0340. K₂Na₂IrO₄] crystallizes in a new type of structure. The oxide is antiferromagnetic as magnetic measurements showed (T_N = 32 K, Θ = ?60.2 K (single crystals) and ?49.2 K (powder) respectively, μ = 3.06 μ_B (single crystals) and 2.93 μ_B (powder) respectively). Effective coordination numbers ECoN, mean fictive ionic radii MEFIR and the Madelung part lattice energy MAPLE as well as the charge distributions CHARDI and CHARDINO are calculated and discussed.