Ein neues Oxotantalat(V): Über KLi6[TaO6] [1]

A New Oxotantalate(V): On KLi₆[TaO₆] [1] For the first time hitherto unknown KLi₆[TaO₆] was obtained by intimately pulverized mixtures of K₂O, Li₂O and Ta₂O₅ (molar ratio K:Li:Ta = 1.1:6.6:1) in a closed Ni-cylinder (800°C, 30 d) in form of colourless single crystals; trigonal-rhomboedral (space group R3 m) with a = 822.6(1) pm, c = 721.2(1) pm (Guinier-Simonpowder data), Z = 3. The determination of the crystal structure (four cycle diffractometer data, 224 out of 224 I₀ (hkl), R = 1.80%, R_w = 1.79%, absorption not considered) proves that KLi₆[TaO₆] is isotypic with KLi₆[IrO₆], a stuffed derivative of the α-Li₆[UO₆] structure type. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, the latter derived from Mean Effective Ionic Radii, MEFIR, as well as the Charge Distribution, CHARDI, are calculated and discussed.