EPR characterization of half-integer-spin iron molecule-based magnets

We report single crystal high-frequency electron paramagnetic resonance studies of two recently discovered half-integer Fe₇ complexes: Fe₇O₃(O₂CBu^t)₉(mda)₃(H₂O)₃] (1) and Fe₇O₄(O₂CPh)₁₁(dmem)₂] (2). The obtained spectra confirm spin S = 5/2 ground states for both complexes. On the basis of detailed frequency and field orientation dependent studies, we find that complex 1 is a single-molecule magnet (uniaxial zero-field-splitting parameter, D < 0) while complex 2 is not (D > 0). The EPR linewidth for complex 1 is considerably narrower in comparison to spectra obtained for other single-molecule magnets, suggesting the possibility of reduced decoherence from nuclear spins (⁵⁶Fe has no nuclear moment).