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 Mn12-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 Mn12-Ac. Indeed, the HFEPR spectra for Mn12-BrAc and Mn12-tBuAc provide spectacular resolution, allowing for unique spectroscopic insights into high-symmetry giant spin SMMs.

A multi-high-frequency/high-field EPR technique is used to study single crystal samples of three high-symmetry Mn12 single-molecule magnets (SMMs): Mn12-Ac, Mn12-BrAc and Mn12-tBuAc. The two newer complexes (Mn12-BrAc and Mn12-tBuAc) show much sharper EPR peaks, and none of the fine structures seen for the Mn12-Ac complex, thus confirming that the acetic acid solvent significantly influences the properties of this well studied SMM. Indeed, the EPR spectra for Mn12-BrAc and Mn12-tBuAc provide spectacular resolution, allowing for unique spectroscopic insights into high-symmetry giant spin SMMs.Figure optionsDownload as PowerPoint slide