Ba₂ErCl₇: A NEW TERNARY RARE EARTH CHLORIDE WITH BARIUM. M. S. Wickleder, Ph. Egger and J. Hulliger, Institute for Inorganic Analytical and Physical Chemistry, University of Berne, Freiestr. 3, 3012 Berne, Switzerland

Our search for new erbium based upconversion materials has lead to the new compound Ba₂ErCl₇ with isolated sevenfold coordinate Er³⁺ ions within a network of edge and corner sharing [BaCl₉] polyhedra. The [ErCl₇] polyhedron can be described as a monocapped trigonal prism which, due to the site symmetry C₁ of the Er³⁺ ions in the space group P2₁/c, is slightly distorted (for the crystallographic data see table 1). The structure contains two crystallographically different Ba²⁺ ions (Ba1 and Ba2). Each of them is ninefold coordinated by Cl^- ions and the [BaCl₉] polyhedra are linked to form chains running along the c-axis (Ba1) and the a-axis (Ba2), respectively. The chains are connected to form a three dimensional network that contains the Er³⁺ ions.

Tab.1 Crystallographic Data for Ba₂ErCl₇