Strong antiferromagnetic coupling at long distance through a ligand to metal charge transfer mechanism

The use of large substituted oligoacenes with dicyanoamido groups as bridging ligands should allow one to design new dinuclear transition metal complexes with relatively strong exchange interactions at very long intermetallic distances. Theoretical methods based on density functional theory predict antiferromagnetic exchange coupling constants of around 200 cm(-1) for a nonacene Cr-III complex with an intermetallic distance of 33 angstrom, due to a ligand-metal charge-transfer mechanism. In contrast, the isoelectronic V-II complex in which such electron-transfer process is not allowed shows a weak ferromagnetic coupling.