Tuning anisotropy barriers in a family of tetrairon(III) single-molecule magnets with an S=5 ground state

The first family of rare-earth-based single chain magnets is presented. Compounds of general formula [M(hfac)(3)(NITPhOPh)], where M) Eu, Gd, Tb, Dy, Ho, Er, or Yb, and PhOPh is the nitronylnitroxide radical (2,4'-benzoxo-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), have been structurally characterized and found to be isostructural. The characterization of both static and dynamic magnetic properties of the whole family is reported. Dy, Tb, and Ho compounds display slow relaxation of the magnetization, and ac susceptibility shows a thermally activated regime with energy barriers of 69, 45, and 34 K for Dy, Tb, and Ho compounds, respectively, while only a frequency-dependent susceptibility is observed for Er below 2.0 K. In Gd and Yb derivatives, antiferromagnetic interactions dominate. The pre-exponential factors differ by about 4 orders of magnitude. Finite size effects, due to naturally occurring defects, affect the static and dynamic properties of the compounds differently.