Mn-4 single-molecule magnets with a planar diamond core and S=9

摘要

The syntheses and magnetic properties are reported for three Mn-4 single-molecule magnets (SMMs): [Mn-4(hmp)(6)(NO3)(2)(MeCN)(2)](ClO4)(2).2MeCN (3), [Mn-4(hmp)(6)(NO3)(4)].(MeCN) (4), and [Mn-4(hmp)(4)(acac)(2)(MeO)(2)](ClO4)(2).2MeOH (5). In each complex there is a planar diamond core of Mn-2(III) Mn-2(II) 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 Mn-2(III) Mn-2(II) 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. (C) 2003 Elsevier Science Ltd. All rights reserved. [References: 26]