Evidence for the S=9 excited state in Mn12-bromoacetate measured by electron paramagnetic resonance -: art. no. 054426

We present high-frequency high-field electron paramagnetic resonance (EPR) measurements on the [Mn12O12(O2CCH2Br)(16)(H2O)(4).4CH(2)Cl(2)] dodecanuclear manganese complex (Mn-12-BrAc). The crystal-field parameters are found to be very similar to those of the original compound Mn-12-acetate ([Mn12O12(O2CCH3)(16)(H2O)(4)]). A detailed analysis of the frequency and temperature dependence of anomalous peaks observed in the EPR spectra of Mn-12-BrAc enables us to locate the S=9 manifold at about 40 K above the M-S=+/-10 ground state of this nominally S=10 system. This is very close to the M-S=+/-6 state of the S=10 manifold, thus suggesting pathways for the thermally assisted magnetization dynamics and related properties. Finally, the EPR fine structures recently attributed to disorder associated with the acetic acid of crystallization in Mn-12-Ac are absent in the present measurements, thus suggesting that the Mn-12-BrAc complex represents a more suitable candidate for measurements of quantum effects in high symmetry S=10 SMMs.