Structure of some thallium lanthanide double molybdates of composition TlLn(MOO4)2

Two polymorphs of TlLn(MoO4)(2) (Ln = Eu, Sm, Pr) double molybdates are structurally studied using the Rietveld method. Layered alpha-TlLn(MoO4)(2) crystallize in orthorhombic space group Pbcn (Z = 4) and are isostructural to KY(MoO4)(2). Layers are formed of LnO(8) eight-vertices and MoO4 tetrahedra. Tl+ cations (CN = 10) are distributed between layers. gamma-TlLn(MoO4)(2) (Ln = Sm, Pr) and beta-TlEu(MoO4)(2) crystallize in tetragonal space group P4/nnc (Z = 2). The structures are frameworks. Thallium cations, coordinated by eight oxygen atoms, reside in windows of the framework built of LnO(8) polyhedra and MoO4 tetrahedra.