New mixed-valence ternary bromides and iodides of dysprosium and thulium of the type A(5)M(3)X(12)

The new ternary mixed-valence bromides and iodides of dysprosium and thuliu m Rb5Dy3BT12, Rb5Tm3Br12, K5Dy3I12, K5Tm3I12, Rb5Dy3I12 and Rb5Tm3I12 were obtained by metallothermic reduction of DyBr3, TmBr3, DyI3 and TmI3, respec tively, with potassium and rubidium in the presence of the respective alkal i metal halides in sealed niobium containers. The crystal structure was det ermined for the example of K5Dy3I12 (hexagonal, P (6) over bar 2m, Z = 1; a = 1446.7(2), c = 473.3(1) pm): DyI6 octahedra are connected via common tra ns edges to chains. Magnetic measurements on X-ray pure samples show Curie- Weiss behaviour at sufficiently high temperatures. Antiferromagnetic coupli ng occurs at low temperatures.