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.