Syntheses and crystal structures of new alkali metal rare-earth tellurides of the compositions KLnTe2 (Ln = La, Pr, Nd, Gd), RbLnTe2 (Ln = Ce, Nd) and CsLnTe2 (Ln = Nd)

Of the compounds ALnQ(2) (A = Na, K, Rb, Cs; Ln = rare earth-metal; Q = S, Se, Te) the crystal structures of the new tellurides KLaTe2, KPrTe2, KNdTe2, KGdTe2, RbCeTe2, RbNdTe2, and CsNdTe2 were determined by single-crystal X-ray analyses. They all crystallize in the alpha-NaFeO2 type with space group Rim and three formula units in the unit cell. The lattice parameters are: KLaTe2: a = 466.63(3) pm, c = 2441.1(3) pm; KPrTe2: a = 459.73(2) pm, c = 2439.8(1) pm; KNdTe2 : a = 457.83(3) pm, c = 2443.9(2) pm; KGdTe2: a = 449.71(2) pm, c = 2443.3(1) pm; RbCeTe2: a = 465.18(2) pm, c = 2533.6(2) pm; RbNdTe2: a = 459.80(3) pm, c = 2536.5(2) pm, and CsNdTe2: a = 461.42(3) pm, c = 2553.9(3) pm. Characteristics of the alpha-NaFeO2 structure type as an ordered substitutional variant of the rock-salt (NaCl) type are layers of corner-sharing [(A(+)/Ln(3+))(Te2-)(6)] octahedra with a layerwise alternating occupation by the cations A(+) and Ln(3+).