A Study of Magnetic Relaxation in Dysprosium(III) Single-Molecule Magnets.

Although the development of single-molecule magnets (SMMs) is rapid, there are only two families of high energy barrier (U ) dysprosium(III) SMMs known so far: the cyclopentadienyl (Cp) family with a sandwich structure and the pentagonal-bipyramidal (PB) family with D symmetry. These high-barrier SMMs, which usually possess U >500 cm allow the separate study of the four magnetic relaxation paths, namely, direct, quantum tunnelling, Raman and Orbach processes, in detail. Whereas the first family is chemically more challenging to modify the Cp rings, it is shown herein that the latter family, with the common formulae [DyX X (L ) ] , such as X /X = OCMe , OSiMe , OPh, Cl or Br ; L =THF/pyridine/4-methylpyridine, can be readily fine-tuned with a range of axial and equatorial ligands by simple substitution reactions. This allows unambiguous confirmation that the U mainly depends on the identity of X and X , rather than on L . More importantly, the fitted parameters are barrier dependent. If X is an O donor and X is a halide, 500