Squarato-Metal(II) complexes. 2. Unusual bonding mode for a squarato-bridged trinuclear Copper(II) complex

摘要

Herein, we report the structural characterization and magnetic properties of the unique squarato-bridged-tricopper(II) complex, [Cu-3(pmaP)(3)(mu(1,2,3)-C4O4)](ClO4)(4)center dot 2H(2)O (1), based on the tripod tripyridylamine ligand bis[2-(2-pyridyl)ethyl)(2-pyridyl)methylamine (pmap). Each of the three copper centers is penta-coordinated by tour N atoms of a pmap ligand and one bridging 0 atom of the central squarato dianion. This complex is the first example of a nonpolymeric X-ray structurally characterized trimeric transition metal complex with the three metal cations being bridged by a single squarato ligand in a mu(1,2,3) coordination mode. The magnetic properties of the complex were measured over the temperature range 2-300 K. The complex exhibits moderate bulk antiferromagnetic interaction. The three magnetic exchange pathways have J values of -27.8,- -20.8, and -31.9 cm(-1). The DFT calculations corroborate the relatively strong antiferromagnetic couplings obtained from the fitting of the experimental magnetic susceptibility data and allow an assignment of the fitted J values. Several geometrical parameters have been analyzed using theoretical calculations to establish magnetostructural correlations for complex 1.