Butterfly M<sub>2</sub><sup>III</sup>Er<sub>2</sub> (M<sup>III</sup> = Fe and Al) SMMs: Synthesis, Characterization, and Magnetic Properties

The reaction of <i>N</i>-(2-pyridylmethyl)­iminodiethanol (H<sub>2</sub>L, pmide), FeCl<sub>2</sub>·4H<sub>2</sub>O or AlCl<sub>3</sub>·6H<sub>2</sub>O with ErCl<sub>3</sub>·6H<sub>2</sub>O and <i>p</i>-Me-PhCO<sub>2</sub>H in the ratio of 2:1:1:4 in the presence of Et<sub>3</sub>N in MeOH and MeCN yielded compounds [Fe<sub>2</sub>Er<sub>2</sub>(μ<sub>3</sub>-OH)<sub>2</sub>(pmide)<sub>2</sub>(<i>p</i>-Me-PhCO<sub>2</sub>)<sub>6</sub>]·2MeCN (<b>1</b>) and [Al<sub>2</sub>Er<sub>2</sub>(μ<sub>3</sub>-OH)<sub>2</sub>(pmide)<sub>2</sub>(<i>p</i>-Me-PhCO<sub>2</sub>)<sub>6</sub>]·2MeCN (<b>2</b>). These two complexes are isostructural, possessing a planar butterfly motif with the Er<sup>III</sup> ions in the wingtip positions. Both compounds show single molecule magnet (SMM) behavior. For the [Al<sub>2</sub>Er<sub>2</sub>] compound, the slow relaxation of the magnetization under zero applied direct current (dc) field does not show maxima, but the relaxation processes could be analyzed using an applied dc field of 1000 Oe. In-depth alternating current measurements under different dc fields on the [Fe<sub>2</sub>Er<sub>2</sub>] compound reveals that the Fe–Fe and Fe–Er interactions speed up the relaxation and decrease the energy barrier height of the SMM in comparison with the [Al<sub>2</sub>Er<sub>2</sub>] case.