Syntheses and structures of the new quaternary rubidium selenides RbLn2CuSe4 (Ln = Sm, Gd, Dy), Rb1.5Ln2Cu2.5Se5 (Ln = Gd, Dy), and RbSm2Ag3Se5

Six quaternary rubidium selenides RbLn(2)CuSe(4) (Ln = Sm, Gd, Dy), Rb(1.5)Ln(2)Cu(2.5)Se(5) (Ln = Gd, DS), and RbSm2Ag3Se5 have been synthesized at 1073 K with the use of a reactive flux of Rb2Se3. At 153 K all compounds contain four formula units in orthorhombic unit cells. The isostructural compounds RbLn(2)CuSe(4) crystallize in space group Cmcm; the isostructural compounds Rb(1.5)Ln(2)Cu(2.5)Se(5) crystallize in space group Pnnm; RbSm2Ag3Se5 crystallizes in space group Cmcm. The cells of RbLn(2)CuSe(4) are (Ln, a, b, c (Angstrom)): Sm, 4.1834(9), 14.308(3), 14.439(3); Gd, 4.1568(8), 14.227(3), 14.409(3); Dy, 4.1237(10), 14.083(4), 14.291(3), and the corresponding R-1 indices for the refined structures are 0.023, 0.029, and 0.039. The cells of Rb(1.5)Ln(2)Cu(2.5)Se(5) are: Gd, 16.243(3), 16.449(3), 4.0980(7); Dy, 16.120(3), 16.292(3), 4.0610(8), and the R-1 indices are 0.036 and 0.043. The cell of RbSm2Ag3Se5 is 4.3223(6), 15.229(2), 17.420(3) Angstrom and the R-1 index is 0.025. All six are closely related three-dimensional tunnel structures. Their anionic frameworks are built from LnSe(6) octahedra and MSe4 (M = Cu, Ag) tetrahedra. RbLn(2)CuSe(4) contains infinite (1)(proportional to)[CuSe3] chains of vertex-sharing tetrahedra; Rb(1.5)Ln(2)Cu(2.5)Se(5) also contains infinite chains of tetrahedra; and the tunnel in RbSm2Ag3Se5 holds one Rb+ cation in a 10-membered ring consisting of six Ag-Se bonds and four Sm-Se bonds. Rb1.5Dy2Cu2.5Se5, which is paramagnetic, obeys the Curie-Weiss law and has an effective magnetic moment of 10.63(4) mu(B). (C) 2000 Academic Press.