Squarato−Metal(II) Complexes. 2. Unusual Bonding Mode for a Squarato-Bridged Trinuclear Copper(II) Complex

Herein, we report the structural characterization and magnetic properties of the unique squarato-bridged-tricopper(II) complex, [Cu3(pmap)3(μ1,2,3-C4O4)](ClO4)4·2H2O (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 four N atoms of a pmap ligand and one bridging O atom of the central squarato dianion. This complex is the first example of a non-polymeric X-ray structurally characterized trimeric transition metal complex with the three metal cations being bridged by a single squarato ligand in a μ1,2,3 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.