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

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-Bu4N+ 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 dx2−y2 symmetry) and [Ni(cyclam)]2+ (with dx2−y2 and dz2 symmetry) have the same eg symmetry. The experimental exchange interaction deduced from the fit of the magnetic susceptibility (Jexp/kB = +5.0 K) was confirmed by theoretical calculations (Jcalc/kB = +7.3 K), and a rationale is given for the presence of an intrachain ferromagnetic interaction.