Redox Switching of Magnetic Anisotropy in Copper(II) Verdazyl Systems

Reaction of copper(II) triflate with 1-isopropyl-3,5-di(2′-pyridyl)-6-oxo-2H-tetrazine (dipyvdH) and triethylamine gave the neutral species [Cu(dipyvd)2]. [Cu(dipyvd)2] can be oxidized in two one-electron steps, leading to [Cu(dipyvd)2]+ and [Cu(dipyvd)2]2+ isolated as their PF6– salts. All three species are best formulated as copper(II) compounds with localized anionic diamagnetic, or neutral radical ligands. Exchange coupling between the neutral radical ligands and the copper(II) ion is strongly ferromagnetic, leading to S = 1 and S = 3/2 ground states for [Cu(dipyvd)2]+ and [Cu(dipyvd)2]2+, respectively. High-field/high-frequency EPR (HF-EPR) measurements reveal that, upon oxidation, the copper(II) complexes become anisotropic, with zero-field splitting (ZFS) parameters of D = 4.5 cm–1, E/D = 0.04 for [Cu(dipyvd)2]+ and D = 1.5 cm–1, E/D = 0.3 for [Cu(dipyvd)2]2+. DFT calculations suggest that the major component of the ZFS tensor for [Cu(dipyvd)2]+ is aligned with the Jahn–Teller elongation axis of the cations.