Single‐Ion Magnetic Behaviour in an Iron(III) Porphyrin Complex: A Dichotomy Between High Spin and 5/2–3/2 Spin Admixture
Marta Viciano‐Chumillas, Geneviève Blondin, Martin Clémancey, J. Krzystek, Mykhaylo Ozerov, Donatella Armentano, Alexander Schnegg, Thomas Lohmiller, Joshua Telser, Francesc Lloret, Joan Cano
Abstract
Abstract A mononuclear iron(III) porphyrin compound exhibiting unexpectedly slow magnetic relaxation, which is a characteristic of single‐ion magnet behaviour, is reported. This behaviour originates from the close proximity (≈550 cm −1 ) of the intermediate‐spin S= 3/2 excited states to the high‐spin S= 5/2 ground state. More quantitatively, although the ground state is mostly S= 5/2, a spin‐admixture model evidences a sizable contribution (≈15 %) of S= 3/2 to the ground state, which as a consequence experiences large and positive axial anisotropy ( D= +19.2 cm −1 ). Frequency‐domain EPR spectroscopy allowed the m S = |±1/2⟩→|±3/2⟩ transitions to be directly accessed, and thus the very large zero‐field splitting in this 3d 5 system to be unambiguously measured. Other experimental results including magnetisation, Mössbauer, and field‐domain EPR studies are consistent with this model, which is also supported by theoretical calculations.