title: K2Ln2As2Se9 (Ln = Sm, Gd): the first quaternary rare-earth selenoarsenate compounds with a 3D framework containing chairlike As2Se4 units.
abstract: The new compounds K(2)Ln(2)As(2)Se(9) (Ln = Sm, Gd) were obtained by applying the reactive flux method. The structure consists of a three-dimensional (3D) [Ln(2)As(2)Se(9)](2-) framework with K(+) ion-filling tunnels running along the b axis. The two unique Ln(3+) cations are coordinated by two Se(2)(2-) dumbbells, two AsSe(3)(3-) pyramids, and one chairlike As(2)Se(4)(2-) unit in a bicapped trigonal-prismatic geometry. The Ln(3+)-centered trigonal prisms share triangular faces with neighboring prisms, forming one-dimensional chains along the b axis. These chains are linked to each other to form layers by sharing Se(2-) anions on the capped sites of the trigonal prisms. The As(2)Se(4) units connect these layers to form the 3D framework.
authors.affiliation: Institut für Anorganische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstrasse 40 (Otto-Hahn Platz 6-7), D-24098 Kiel, Germany.
authors.forename: Yuandong
authors.initials: Y
authors.lastname: Wu
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bensch