Crystal structure and magnetic properties of Cu3(TeO3)2Br2 -: a layered compound with a new Cu(II) coordination polyhedron

The new compound Cu-3(TeO3)(2)Br-2 crystallizes in the monoclinic spacegroup C2/m. The unit cell parameters are a = 9.3186(18)angstrom, b = 6.2781(9)angstrom, c = 8.1999(16)angstrom, beta = 107.39(2)degrees, 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 [CuO4] Coordination and one showing an unusual [CuO4Br] trigonal bi-pyramidal coordination, the Br-ion is located in the equatorial plane. The Te(IV) atom has a tetrahedral [TeO3E] coordination where E is the 5s(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. (c) 2005 Elsevier Inc. All rights reserved.