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 reported where R is [GRAPHICS] 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, Chi(M)''. Some samples show one Chi(M)'' peak in the 5-6 K range, others show a Chi(M)'' peak in the 2-3 K range, and even other compounds show both peaks. These X-M'' 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 Chi(M)'' peaks are given. Hysteresis loops are seen below similar to 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.