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) Å3, Dx = 3.436, λ(MoKα1) = 0.7093 Å, μ = 113.9 cm-1, Rw(F2) = 0.060 for 2613 observations and 66 variables, R(F) = 0.022 for 2534 observations having F2o > 2σ(F2o); 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) Å3, Dx = 4.590, λ(MoKα1) = 0.7093 Å, μ = 267.8 cm-1, Rw (F2) = 0.100 for 3083 observations and 66 variables, R(F) = 0.041 for 2965 observations having F2o > 2σ(F2o). 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.