Mn4 single-molecule magnets with a planar diamond core and S=9

Abstract

The syntheses and magnetic properties are reported for three Mn4 single-molecule magnets (SMMs): [Mn4(hmp)6(NO3)2(MeCN)2](ClO4)2·2MeCN (3), [Mn4(hmp)6(NO3)4]·(MeCN) (4), and [Mn4(hmp)4(acac)2(MeO)2](ClO4)2·2MeOH (5). In each complex there is a planar diamond core of MnIII2MnII2 ions. An analysis of the variable-temperature and variable-field magnetization data indicate that all three molecules have intramolecular ferromagnetic coupling and a S=9 ground state. The presence of a frequency-dependent alternating current susceptibility signal indicates a significant energy barrier between the spin-up and spin-down states for each of these three MnIII2MnII2 complexes. The fact that these complexes are SMMs has been confirmed by the observation of hysteresis in the plot of magnetization versus magnetic field measured for single crystals of complexes 3 and 4. The hysteresis loops for both of these complexes exhibit steps characteristic of quantum tunneling of magnetization. Complex 4 shows its first step at zero field, whereas the first step for complex 3 is shifted to −0.10 T. This shift is attributable to weak intermolecular antiferromagnetic exchange interactions present for complex 3.