Slow magnetic relaxation in dinuclear dysprosium and holmium phenoxide bridged complexes: a Dy2 single molecule magnet with a high energy barrier

Abstract

Dinuclear [M(H₃L^1,2,4)]₂ (M = Dy, Dy₂; M = Ho, Ho₂) complexes were isolated from an heptadentate aminophenol ligand. The crystal structures of Dy₂·2THF, and the pyridine adducts Dy₂·2Py and Ho₂·2Py, show that the complexes are dinuclear, with unsupported double phenoxide bridges, and that the N₄O₄ environment of the Ln^III centres is distorted triangular dodecahedral. The magnetic analysis of Dy₂ and Ho₂ shows that Dy₂ is a single molecular magnet (SMM), with a thermal-activated zero-field effective energy barrier (U_eff) of 367.7 K, the largest barrier shown by double phenoxide-bridged dinuclear dysprosium complexes to date. Ho₂ is one of the scarce dinuclear complexes showing frequency-dependence for the out-of-phase component of susceptibility, although it does not even show field-induced SMM behaviour above 2 K. Ab initio calculations were performed in order to shed light on the magnetic dynamics of the complexes, and these studies support the experimental magnetic results.