A comparison between high-symmetry Mn₁₂ single-molecule magnets in different ligand/solvent environments

We present angle-resolved high-frequency electron paramagnetic resonance (HFEPR) data collected for single-crystal samples of deuterated and undeuterated Mn₁₂-acetate. The spectra reveal fine structures associated with the various Mn₁₂ species corresponding to the different local solvent environments proposed by Cornia et al. [A. Cornia, R. Sessoli, L. Sorace, D. Gatteschi, A.L. Barra, C. Daiguebonne, Phys. Rev. Lett. 89 (2002) 257201], and recently confirmed by Hill et al. [S. Hill, R.S. Edwards, S.I. Jones, J.M. North, N.S. Dalal, Phys. Rev. Lett. 90 (2003) 217204] and del Barco et al. [E. del Barco, A.D. Kent, E.M. Rumberger, D.N. Hendrickson, G. Christou, Phys. Rev. Lett. 91 (2003) 047203]. Each of the fine structures exhibits a distinct dependence on the applied field orientation, thereby highlighting the discrete nature of the disorder. We then compare these data with spectra obtained for two recently discovered high-symmetry (S₄) analogs of Mn ₁₂-Ac, differing only in their ligand and solvent structures. None of the highly reproducible fine-structures seen in the Mn₁₂-Ac samples are found for the new Mn₁₂ complexes, thus confirming the idea that the solvent structure significantly influences the QMT dynamics in Mn ₁₂-Ac. Indeed, the HFEPR spectra for Mn₁₂-BrAc and Mn ₁₂-tBuAc provide spectacular resolution, allowing for unique spectroscopic insights into high-symmetry giant spin SMMs.