Single-Molecule Magnets: Magnetization Relaxation and Quantum Tunneling in Dodecanuclear Manganese Complexes

The syntheses and characterization of three new dodecanuclear manganese complexes with the composition [Mn12O12(O2CR)16(H2O)4] are Complexes 1-3 can be prepared with different solvate molecules in the crystal. The X-ray structure of 1–8(CH2Cl2) (1a) has been determined. The nature of the solvation influences the out-of-phase AC magnetic susceptibility, χm ″ Some samples show one χm ″ peak in the 5–6 K range, others show a χm ″ peak in the 2–3 K range, and even other compounds show both peaks. These χm ″ peaks are indicative of a slow relaxation of a single-molecule magnet, where the magnetization of the molecule cannot keep in phase with the oscillating AC magnetic field. Possible explanations for the two χm ″ peaks are given. Hysteresis loops are seen below −2.5 K. Step-like features are seen on the hysteresis loops measured for a single crystal of the R = Et (6) complex. Quantum mechanical tunneling could be the origin of these step-like features.