Single Molecule Magnets (SMM), which at low temperature behave as tiny magnets at the molecular scale, have attracted enormous interest in recent years, and the switching of their magnetic caracteristics is also raising more and more attention. If few examples of redox modulation have been reported so far, a total, robust, and reversible photo-switching process remains to be achieved with 4f-based SMM. On the other hand, photo-induced change of the coordination environment of lanthanide ions has been demonstrated upon the photoisomerization of spiropyran or spirooxazine ligands. Such isomerization induces large changes in the relaxivity or the luminescence of the complexes. Consequently, lanthanide complexes based on spiropyran ligands are ideal candidates for the photo-control of slow relaxation of magnetization since spiropyran (SP) to merocyanine (MC) isomerization is expected to lead to drastic modifications in the lanthanide ion environment and in fine, in the related magnetic properties. We demonstrate herein that the SP moiety is a useful precursor for the synthesis of unique lanthanide complexes that display SMM properties. Indeed, starting with tris(hexafluoroacetylacetonate)lanthanide precursors and a bis(2-pyridinemethyl)amine substituted spiropyran ligand, this strategy afforded non-photochromic Y, Yb and Dy complexes that bear a MC ligand and display an unprecedented N3O5 environment (figure 1). On the basis of ab initio calculations, a very strong axial magnetic anisotropy of the dysprosium complex can be predicted for such environment and explained by the presence of a highly charged phenolate oxygen that belongs to the MC ligand. We therefore rationalize why this N3O5 environment lead to a great SMM behavior with a hysteresis loop at 2 K and an energy barrier of 216 K. Further realizations to reach photochromic lanthanide complexes with SMM behavior will also be presented.

Highly axial magnetic anisotropy in a N3O5 dysprosium(III) coordination environment generated by a merocyanine ligand

253rd National Meeting (2017)

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