Cyclooctatetraenide-based single-ion magnets featuring bulky cyclopentadienyl ligand.

We report a family of organometallic rare-earth complexes with the general formula (COT)M(Cp) (where (COT) = cyclooctatetraenide, (Cp) = 1,2,4-tri(-butyl)cyclopentadienide, M = Y(iii), Nd(iii), Dy(iii) and Er(iii)). Similarly to the prototypical Er(iii) analog featuring pentamethylcyclopentadienyl ligand (Cp*), (COT)Er(Cp) behaves as a single-ion magnet. However, the introduction of the sterically demanding (Cp) imposes geometric constraints that lead to a simplified magnetic relaxation behavior compared to the (Cp*) containing complexes. Consequently, (COT)Er(Cp) can be viewed as a model representative of this organometallic single-ion magnet architecture. In addition, we demonstrate that the increased steric profile associated with the (Cp) ligand permits preparation, structural characterization and interrogation of magnetic properties of the early-lanthanide complex, (COT)Nd(Cp). Such a mononuclear derivative could not be obtained when a (Cp*) ligand was employed, a testament to larger ionic radius of this early lanthanide ion.