The first tetranuclear complex with a (μ-CrO4-O,O′,O") bridge:: Crystal structure and ferromagnetic behavior of [{Cu(bpy)2}3(μ-CrO4)](ClO4)4•H2O

A novel tetranuclear complex [{Cu(bpy)(2)}(3)(mu-CrO4)](ClO4)(4).H2O (1) with a (mu-CrO4-O,O',O") bridge has been synthesized by the reaction of K2CrO4 with Cu(ClO4)(2).6H(2)O and bpy in CH3CN/H2O solution (bpy = 2,2'-bipyridine), A single crystal X-ray diffraction analysis showed that the chromate ion bridges three copper(IT) ions showing a pesudo-C-3v symmetry. The coordination sphere of each copper(II) ion is best described as trigonal bipyramidal, implying that the magnetic orbital of copper(II) ion is d(z)2, which is also confirmed by the powder ESR spectra, Variable-temperature magnetic studies verify the validity of the chromate bridging unit to link the tricopper system with ferromagnetic coupling, with 2J = +1.8 cm(-1). ((C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002).