Crystal structure and magnetic properties of Cu 3(TeO 3) 2Br 2—a layered compound with a new Cu(II) coordination polyhedron

Abstract

The new compound Cu 3(TeO 3) 2Br 2 crystallizes in the monoclinic spacegroup C 2 / m . The unit cell parameters are a = 9.3186 ( 18 ) Å , b = 6.2781 ( 9 ) Å , c = 8.1999 ( 16 ) Å , β = 107.39 ( 2 ) ° , Z = 2 . The structure is solved from single crystal data, R 1 = 0.021 . The new compound shows a layered structure where only weak van der Waals interactions connect the layers. There are two crystallographically different Cu(II) atoms; one having a square planar [CuO 4] coordination and one showing an unusual [CuO 4Br] trigonal bi-pyramidal coordination, the Br-ion is located in the equatorial plane. The Te(IV) atom has a tetrahedral [TeO 3 E] coordination where E is the 5 s 2 lone-pair. Within the layers the Cu-polyhedra are connected by corner- and edge sharing to form chains. The chains are separated by the Te atoms. The magnetic properties are dominated by long range magnetic ordering at T c = 70 K . Evidence for a coexistence of ferromagnetic and antiferromagnetic interactions exists.