Synthesis, crystal structure and magnetic properties of [Cr2CU2(bpy)4(ox)5]•2H2O.: An oxalato-bridged heterometallic tetramer

A new heterometallic tetramer of formula [Cr2Cu2(bpy)(4)(ox)(5)].2H(2)O (1) (bpy = 2,2'-bipyridine; ox = oxalate dianion) has been prepared and characterised by single-crystal X-ray diffraction, magnetic susceptibility measurements and ESR spectroscopy. The tetranuclear unit in 1 can be viewed as the combination of two terminal [Cr(bpy)(2)(ox)](-) units with a central oxalato-bridged copper(II) dimer. The chromium ions are in a distorted octahedral environment with metal-ligand distances ranging from 1.944(4) to 2.064(5) Angstrom. The copper(II) centres lie in an axially distorted octahedron. The axial positions are occupied by one oxygen atom belonging to the central bridging oxalate anion [O(9)-Cu(1): 2.245(5) Angstrom] and one oxygen atom coming from the [Cr(bpy)(2)(ox)](-) moiety [O(7)-Cu(1): 2.357(5) Angstrom]. The N2O2 equatorial environment is formed by a bpy ligand [Cu-N mean distance: 1.989(6) Angstrom] and the remaining oxygen atoms [Cu-O mean distance: 2.162(5) Angstrom]. The magnetic properties of 1 have been investigated in the 2-300 K temperature range. A ferromagnetic interaction between the copper(II) centres (J(1) = +2 cm(-1)) is observed, whereas the interaction between the adjacent chromium(III) and copper(II) cations is weakly antiferromagnetic (J(2) = -0.65 cm(-1)). (C) 2003 Elsevier Ltd. All rights reserved.