Due to the slow relaxation of their magnetic moment in the absence of a magnetic field single-molecule magnets (SMMs) open new possibilities in high-density data storage, spintronic devices as well as quantum computing. Lanthanides are particularly desirable in this context as they possess inherently high-magnetic moment as well as high barrier to loss of magnetic information if placed in the appropriate coordination environment. Achieving such bespoke coordination environment is one of the great challenges in the field and can be achieved either by controlling steric or electronic effects of the ligands. (COT)Ln(Cp*) ((COT)2- = cycloctatetraenide, (Cp*)- = pentamethylcyclopentadienide, Ln = Tb, Dy, Er, Ho, Tm) are an iconic family of organometallic complexes with Er, Dy and Ho derivatives exhibiting SMM behavior. The presence of both (COT)2- and (Cp*)- ligand architectures opens a myriad of ways to alter the coordination environment. However, only electronic tuning of the coordination environment (and associated SMM properties) by exchanging the Cp* ligand with isoelectronic heterocycles with varying electron donor strength has been explored to date. Conversely, tuning of the magnetic properties by the means of steric control is a common method in the field of SMMs. However, this approach has not yet been investigated in the described family of complexes discussed here. In this context, we decided to explore the bulky 1,3,5-tri(tert-butyl)cyclopentadienide anion (Cpttt)- as a replacement for the (Cp*)- present in (COT)Ln(Cp*) SMMs. In comparison with the parent complexes, the (COT)Ln(Cpttt) (M = Dy, Er) species have more rigid structures, which limits the influence of crystal packing effects and rotational freedom of the ligands in the solid state. These lead to better defined magnetic relaxation behavior for the investigated compounds. Furthermore, the access to more sterically demanding coordination environment allows for extension of this series to early lanthanides, exemplified by the preparation and full characterization of (COT)Nd(Cpttt) that acts as a zero-field SMM. The preparation of such derivative with the less bulky (Cp*)- ligand was not possible due to the larger ion radius of lighter elements of the lanthanide series.

Tuning the magnetic properties of a series of lanthanide sandwich complexes using bulkier 1,3,5-tri(tert-butyl)cyclopentadienide ligands

ACS Spring 2022

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