Synthesis, Structures, and Properties of Layered Quaternary Chalcogenides of the General Formula ALnEQ 4 (A = K, Rb; Ln = Ce, Pr, Eu; E = Si, Ge; Q = S, Se)

Four related quaternary compounds containing rare‐earth metals have been synthesized employing the molten flux method and metathesis. The reactions of Eu and Rb 2 S 5 with Si and Ge in evacuated fused silica ampoules at 725 °C for 150 h yielded RbEuSiS 4 ( I ) and RbEuGeS 4 ( II ), respectively. On the other hand, a reaction between CeCl 3 and K 4 Ge 4 Se 10 at 650 °C for 148 h has yielded KCeGeSe 4 ( III ) and KPrSiSe 4 ( IV ) was obtained by the reaction of elemental Pr, Si and Se in KCl flux at 850 °C for 168 h. Crystal data for these compounds are as follows: I , orthorhombic, space group P 2 1 2 1 2 1 (#19), a = 6.392(1), b = 6.634(2), c = 17.001(3) Å, α = β = γ = 90°, Z = 4; II , monoclinic, space group P 2 1 / m (#11), a = 6.498(2), b = 6.689(3), c = 8.964(3) Å, β = 108.647(6)°, Z = 2; III , monoclinic, space group P 2 1 (#4), a = 6.852(2), b = 7.025(2), c = 9.017(3) Å, β = 108.116(2)°, Z = 2; IV , monoclinic, space group P 2 1 (#4), a = 6.736(2), b = 6.943(2), c = 8.990(1) Å, β = 108.262(2)°, Z = 2. The crystal structures of I ‐ IV contain two‐dimensional corrugated anionic layers of the general formula, [LnEQ 4 ] − (Ln = Ce, Pr, Eu; E = Si, Ge and Q = S, Se) alternately piled upon layers of alkali cations. In addition to structural elucidation, Raman and UV‐visible spectroscopy, and magnetic measurements for compound III (KCeGeSe 4 ) are also discussed.