Synthesis and structures of the quaternary chalcogenides of the type KLnMQ₄ (Ln = La, Nd, Gd, Y; M = Si, Ge; Q = S, Se)

Some new quaternary compounds of the type KLnMQ₄ (Ln = La, Nd, Gd, Y; M = Si, Ge; Q = S, Se) have been synthesized by the reaction of K₂S₅ or K₂Se₅ with lanthanide sulfides or selenides and elemental Ge or Si at 1000°C. The crystal structures of two of these compounds have been determined by X-ray diffraction techniques and are isostructural. Crystal data: KLaGeS₄-space group P2₁, M = 378.84, Z = 2, a = 6.653(1), b = 6.679(2), c = 8.643(2) Å, β = 107.57(1)° (T = 115 K), V = 366.1(1) ų, D_x = 3.436, λ(MoKα₁) = 0.7093 Å, μ = 113.9 cm^-1, R_w(F²) = 0.060 for 2613 observations and 66 variables, R(F) = 0.022 for 2534 observations having F²_o > 2σ(F²_o); KLaGeSe₄-space group P2₁, M = 566.44, Z = 2, a = 6.875(3), b = 7.002(2), c = 8.942(4) Å, β = 107.84(2)° (T = 115 K), V = 409.8(3) ų, D_x = 4.590, λ(MoKα₁) = 0.7093 Å, μ = 267.8 cm^-1, R_w (F²) = 0.100 for 3083 observations and 66 variables, R(F) = 0.041 for 2965 observations having F²_o > 2σ(F²_o). The other compounds synthesized appear to crystallize in the same structure type. The structure consists of two-dimensional ²_∞ [LnMQ^-₄] layers separated by K⁺ cations in trigonal prismatic sites. The layers consist of LnQ₇ distorted monocapped trigonal prisms and MQ₄ tetrahedra that share edges and corners. The resultant structure is related to those of Eu₂GeS₄ and ScPS₄. The diffuse reflective UV-visible spectrum of KLaGeS₄ has been measured. From measurements of magnetic susceptibility vs temperature both KNdGeS₄ and KGdGeS₄ show Curie-Weiss behavior.