Ferromagnetic Interactions in Heterobimetallic Chains Formed through the Secondary Coordination of Dithiolene Complexes

Abstract

A novel paramagnetic ( S = 1/2) copper dithiolene complex based on the tfadt ligand (tfadt: 3-trifluoromethyl-acrylonitrile-2,3-dithiolate) is prepared as its n-Bu 4N (+) salt and crystallized with [Ni(cyclam)] (2+) into infinite, one-dimensional chains through CN...Ni interactions, avoiding any direct (antiferromagnetic) overlap between the dithiolene complexes. An unprecedented ferromagnetic interaction within the heterobimetallic chains between the S = 1/2 [Cu(tfadt) 2] (2-) and the S = 1 [Ni(cyclam)] (2+) tectons is observed, despite the fact that the SOMOs of both [Cu(tfadt) 2] (2-) (with d x (2) - y (2) symmetry) and [Ni(cyclam)] (2+) (with d x (2) - y (2) and d z (2) symmetry) have the same e g symmetry. The experimental exchange interaction deduced from the fit of the magnetic susceptibility ( J exp/ k B = +5.0 K) was confirmed by theoretical calculations ( J calc/ k B = +7.3 K), and a rationale is given for the presence of an intrachain ferromagnetic interaction.