Syntheses. structures, and physical properties of the new quaternary rare-earth chalcogenides RbNd2CuS4, RbSm2CuS4, CsLa2CuSe4, CsSm2CuSe4, RbEr2Cu3S5, CsGd2Ag3Se5, CsTb2Ag3Se5, and Rb2Gd4Cu4S9

Eight quaternary rare-earth chalcogenides, RbSm2CuS4, CsLa2CuSe4 CsSm2CuSe4 , KbEr(2)Cu(3)S(5), CsGd2Ag3Se5, CsTb2Ag3Se5, and Rb2Gd4Cu4S9, have been sy nthesized at 973 K with the use of a reactive flux of A,e, (A = Rb, Cs; Q = S, Se). All structural data were obtained at 153 K. The isostructural comp ounds ALn(2)CuQ(4) (Ln = rare earth) crystallize with four formula units in the KGd2CuS4 structure type in space group Cmcm of the orthorhombic system ; the isostructural compounds ALn(2)M(3)Q(5) (M = Cu,Ag) crystallize with f our formula units in the RbSm2Ag3Se5 structure type in space group Cmcm of the orthorhombic system; and Rb,Gd,Cu,S, crystallizes with two formula unit s in space group C2/m of the monoclinic system. The cell dimensions of ALn( 2)CuQ(4) (a, b, c (Angstrom)) are as follows: RbNd2CuS4, 4.0762(3), 13.954( 1), 13.964(1); RbSm2CuS4, 4.0391(3), 13.815(1), 13.860(1); CsLa2CuSe4, 4.31 29(6), 14.959(2), 14.798(2); CsSm2CuSe4, 4.2066(3), 14.6101(9), 14.5164(9), The corresponding R-1 indices for the refined structures are 0.0264, 0.019 6, 0.0258, and 0.0224. The cell dimensions of ALn(2)M(3)Q(5) are as follows : RbEr2Cu3S5, 3.9283(3), 13.897(1), 16.348(1); CsGd2Ag3Se5, 4.2943(4), 15.4 24(1), 17.501(2); CsTb2Ag3Se5, 4.2779(4), 15.429(2), 17.426(2). The R-1 ind ices are 0.0257, 0.0255, and 0.0241. The cell dimensions of Rb2Gd4Cu4S9 (a, b, c (Angstrom), beta (degrees)) is 13.897(1), 3.9883(3), 16.054(1), 109.2 73(1), and the R-1 index is 0.0199. All eight compounds have closely relate d three-dimensional tunnel structures. All alkali metal atoms in the tunnel s are coordinated to eight Q atoms. Their anionic frameworks are built from LnQ(6) octahedra and MQ(4) tetrahedra. ALn(2)CuQ(4) contains (1)(infinity) [Cu-3] chains of vertex-sharing tetrahedra; Rb,Gd,Cu,S, contains (1)(infini ty)[Cu4S8] chains of tetrahedra; and ALn(2)M(3)Q(5) contains (2)(infinity)[ M(3)Q(5)] layers of tetrahedra. Rb2Gd4Cu4S9 and RbEr2Cu3S5 which are parama gnetic, obey the Curie-Weiss law, and have effective magnetic moments of 7. 9(2) mu (B) for Gd3+ and 9.43(5) mu (B) for Er3+. A band gap of 1.94 eV for Rb2Gd4Cu4S9 was deduced from its diffuse reflectance spectrum, and the typ ical 4f-4f optical transitions for Er3+ were found in RbEr2Cu3S5 at about 1 .6, 1.9, and 2.5 eV. (C) 2001 Academic Press.