Dy(4), Dy(5), and Ho(2) Complexes of an N(3)O(2) Aminophenol Donor: A Dy(5)-µ(3)-Peroxide Single Molecule Magnet

The reactivity of the new flexible potentially pentadentate N(3)O(2) aminophenol ligand H(4)L(r) (2,2′-((pyridine-2,6-diylbis(methylene))bis(azanediyl))diphenol) towards different dysprosium salts and holmium(III) nitrate was investigated. Accordingly, this reactivity seems to greatly depend on the metal ion and salt employed. In this way, the reaction of H(4)L(r) with dysprosium(III) chloride in air leads to the oxo-bridged tetranuclear complex [Dy(4)(H(2)L(r))(3)(Cl)(4)(μ(3)-O)(EtOH)(2)(H(2)O)(2)]·2EtOH·H(2)O (1·2EtOH·H(2)O), while the same reaction just changing the chloride salt by the nitrate one renders the peroxo-bridged pentanuclear compound [Dy(5)(H(2)L(r))(2)(H(2.5)L(r))(2)(NO(3))(4)(µ(3)-O(2))(2)]·2H(2)O (2·2H(2)O), where both peroxo ligands seem to come from the fixation and reduction of atmospheric oxygen. However, if holmium(III) nitrate is used instead of dysprosium(III) nitrate, no evidence of a peroxide ligand is observed, and the dinuclear complex {[Ho(2)(H(2)L(r))(H(3)L(r))(NO(3))(2)(H(2)O)(2)](NO(3))} 2.5H(2)O (3·2.5H(2)O) is isolated. The three complexes were unequivocally characterized by X-ray diffraction techniques, and their magnetic properties were analyzed. Thus, while the Dy(4) and Ho(2) complexes do not show magnet-like behavior even in the presence of an external magnetic field, 2·2H(2)O is a single molecule magnet, with an U(eff) barrier of 61.2 K (43.2 cm(−1)). This is the first homonuclear lanthanoid peroxide SMM, which also shows the highest barrier among the reported 4f/3d peroxide zero field SMMs to date.