Oxometallate neuen Typs: Über Ba3NaNbO6 und Ba3NaTaO6

Oxometallates of a new Type: On Ba₃NaNbO₆ and Ba₃NaTaO₆ For the first time in form of colourless, transparent single crystals of Ba₃NaNbO₆ annealed mixtures of BaO, Na₂O and Nb₂O₅, Ba : Na : Nb = 3.3 : 1.1 : 1, Ni-cylinder, 1100°C, 3d] as well as Ba₃NaTaO₆ annealed mixtures of BaO, Na₂O and Ta₂O₅, Ba : Na : Ta = 3.3 : 1.1 : 1, Ni-cylinder, 1100°C, 3d] have been prepared. The crystal structure was solved by fourcycle-diffractometer data Ba₃NaNbO₆: Mo? Kα , 356 out 356 I₀ (hkl), space group R3 c with a = 1026.6(1)pm, c = 1195.3(2)pm (Guinier-Simon powder data), Z = 6, R = 2.4%, R_w = 2.0% and Ba₃NaTaO₆: Ag? Kα , 498 out of 498 I₀ (hkl), space group R3 c with a = 1027.6(1)pm, c = 1196.0(2)pm (Guinier-Simon powder data), Z = 6, R = 4.9%, R_w = 4.4%], parameters see text. The Ba₃M part of structure (M = Nb, Ta) corresponds to a slightly (hexagonal) deformed Nb₃Al arrangement with Na inserted along 001] between adjacent M^v, which are nearly perfectly octahedrally surrounded by 6 O. The structural relations are deduced by Schlegel Diagrams. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, the latter derived from Mean Effective Ionic Radii, MEFIR, as well as Charge Distribution, CHARDI, are calculated.