Syntheses, Structures, and Physical Properties of the New Quaternary Rare-Earth Chalcogenides RbNd_2CuS_4, RbSm_2CuS_4, CsLa_2CuSe_4, CsSm_2CuSe_4, RbEr_2Cu_3S_5, CsGd_2Ag_3Se_5, CsTb_2Ag_3Se_5, and Rb_2Gd_4Cu_4S_9

摘要

Eight quaternary rare-earth chalcogenides,RbNd_2CuS_4,RbSm_2CuS_4 CsLa_2Se_4, CsSm_2Se_4,RbEr_2Cu_3S_5 CsGd_2Ag_3Se_5,CsTb_2Ag_3Se_5,and Rb_2Gd_4Cu_4S_9,have been syn-thesized at 973K with the use of a reactiveflux of A_2Q_3(A=Rb,Cs; Q=S ,Se). All structural data were obtained at 153K.The isostructural compounds Aln_2 CuQ_4 (Ln=rare earth )crystallize tith four formula units in the KGd_2CuS_4 structure type in space group Cmcm of the orthorhombic system; the isortructural compounds Aln_2 M_3Q_5 (M = Cu, Ag) crystallize with four formula units in the RbSm_2Ag_3Se_5 structure type in space group Cmcm of the orthorhombic system; and Rb_2Gd_4Cu_4S_9 crystallizes with two formula units in space group C2/m of the monoclinic system. The cell dimensions of ALn_2CuQ_4 (a, b, c (A)) are as follows:RbNd_2CuS_4, 4.0762(3), 13.954(1), 13.964(1); RbSm_2CuS_4, 4.0391(3), 13.815(1), 13.860(1); CsLa_2CuSe_4, 4.3129(6), 14.959(2), 14.798(2); CsSm_2CuSe_4, 4.2066(3), 14.6101(9), 14.5164(9). The corresponding R_1 indices for the refined sturctures are 0.0264, 0.0196, 0.0258, and 0.0224. The cell dimensions of ALn_2M_3Q_5 are as follows: RbEr_2Cu_3S_5, 3.9283(3), 13.897(1), 16.348(1); CsGd_2Ag_3Se_5, 4.2943(4), 15.424(1), 17.501(2); CsTb_2Ag_3Se_5, 4.2779(4), 15.429(2), 17.426(2). The R_1 indices are 0.0257, 0.0255, and 0.0241. The cell dimensions of Rb_2Gd_4Cu_4S_9 (a, b, c (A), #beta# (deg)) is 13.897(1), 3.9883(3), 16.054(11), 109.273(3), and the R_1 index is 0.0199. All eight compounds have closely related three-dimnsional trnnel structrues. All alkali metal atoms in the tunnels are coordinated to eight Q atoms. Their anionic frameworksare built from LnQ_6 octahedra and MQ_4 tetrahedra. ALn_2CuQ_4 contains _(infinity)~1[CuQ_3]chains of vertex-sharing tetrahedra; Rb_2Gd_4Cu_4S_9 contains _(infinity)~1[Cu_4S_8] chains of tetrahedra; and ALn_2M_3Q_5 contains _(infinity)~2[M_3Q_5] layers of tetrahedra. Rb_2Gd_4Cu_4S_9 and 9.43(5) #mu#_B for Er~(3+). A band gap of 1.94 eV for Rb_2Gd_4Cu_4S_9 was deduced from its diffuse reflectance reflectance spectrum, and the typical 4f-4f optical transitions for Er~(3+) were found in RbEr_2Cu_3S_5 at about 1.6, 1.9, and 2.5 eV.