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Magnetic and 57Fe Mössbauer Study of the Single Molecule Magnet Behavior of a Dy3Fe7 Coordination Cluster
journal contributionposted on 2009-10-05, 00:00 authored by Ghulam Abbas, Yanhua Lan, Valeriu Mereacre, Wolfgang Wernsdorfer, Rodolphe Clérac, Gernot Buth, Moulay T. Sougrati, Fernande Grandjean, Gary J. Long, Christopher E. Anson, Annie K. Powell
The reaction between N-methydiethanolamine (mdeaH2), benzoic acid, FeCl3, and DyCl3 yields a decanuclear coordination cluster, [Dy3Fe7(μ4-O)2(μ3-OH)2(mdea)7(μ-benzoate)4(N3)6]·2H2O·7CH3OH (1) whose single crystal structure exhibits three and seven crystallographically distinct Dy(III) and Fe(III) ions; six of the Fe(III) ions are pseudo-octahedrally coordinated, whereas the seventh has a trigonal-bipyramidal coordination geometry. Both direct current (dc) and alternating current (ac) magnetic susceptibility studies indicate that, upon cooling, intracluster antiferromagnetic interactions are dominant in 1, yielding a ferrimagnetic spin arrangement. The out-of-phase (χ′′) ac susceptibility reveals that 1 undergoes a slow relaxation of its magnetization mainly resulting from the anisotropy of the Dy(III) ions. This slow relaxation has been confirmed both by magnetization measurements on an oriented single crystal of 1 and by the observation of hysteresis loops below 1.9 K. The macroscopic magnetic studies yield an effective energy barrier, Ueff, of 33.4 K for this relaxation, a barrier that is the highest yet reported for a lanthanide(III)-Fe(III) single molecule magnet. The 57Fe Mössbauer spectra of 1 obtained between 3 and 35 K are consistent with the presence of Fe(III) intracluster antiferromagnetic coupling with slow magnetic relaxation relative to the Larmor precession time, thus confirming, on a microscopic scale, the presence of a barrier to the magnetic relaxation below 35 K. Between 55 and 295 K the Mössbauer spectra reveal paramagnetic behavior with six partially resolved quadrupole doublets, one for the trigonal-bipyramidal Fe(III) site and five for the six pseudo-octahedral Fe(III) sites.