ON THE CRYSTAL-CHEMICAL SIMILARITY OF AURIDE AND HALIDE ANIONS

The crystallographic properties of the aurides M(3)AuO and the alkalimetal halide oxides M(3)XO (M = K, Rb, Cs; X = Br, I) are compared. Rb3BrO, Rb3IO, Cs3BrO, and Cs3IO have been prepared and characterized for the first time: Rb3BrO (a = 5.465(1) Angstrom) crystallizes as a cubic anti perovskite, Cs3BrO (a = 7.800(6), c = 7.122(6) Angstrom) and Cs3IO (a = 8.056(3), c = 7.168(3) Angstrom) as hexagonal anti perovskites, Rb3IO (a = 7.889(1), c = 19.640(1) Angstrom) as a hexagonal anti BaTiO3 type. The analysis of bond lengths, molar volumes and the systematic of the crystal structures leeds to the conclusion, that the crystallographic properties of auride- and bromide anions are similar. The radius of the Au- has been found to be 2.2 Angstrom (KZ 12).