Single-molecule magnets (SMMs) have unique properties that open possible applications in high-density data storage, spintronic devices as well as quantum computing. Their defined feature is a slow magnetic relaxation in the absence of an applied field. The combination of the high intrinsic magnetic moment with an uniaxial anisotropy engendered by the coordination environment leads to long magnetization relaxation times, making lanthanide ions desirable platforms for assembly of SMMs. (COT)Ln(Cp*) ((COT)2- = cycloctatetraenide, (Cp*)- = pentamethylcyclopentadienide, Ln = Tb, Dy, Er, Ho,Tm) are a prominent family of organometallic complexes. The unique properties of these late lanthanides together with the imposed coordination environment enables slow relaxation of magnetization for Er, Dy and Ho. The extension of this series to the early lanthanides would be desirable due to their substantially higher natural abundance. However, their synthesis has been proven difficult for this particular set of ligands in part due to an increase of their ionic radius and furthermore, the usage of early lanthanides as SMMs has been so far limited as their complexes rarely exhibit slow relaxation of magnetization in zero field. In principle, such issues could be ameliorated by carefully tailoring the coordination environment around the lanthanide ion. We hypothesized that a higher steric bulk of the ligand in combination with a uniaxial anisotropy and the absence of ligands in the equatorial plane would engender the desired zero-field SMM property for an early lanthanide complex. We decided to explore the bulky (Cpttt)- (1,3,5-tri(tert-butyl)cyclopentadienide anion) as a ligand of choice for the design of neutral Neodymium based SMMs. Our results show that such organometallic complex – (COT)Nd(Cpttt) – exhibits slow magnetic relaxation without applied external magnetic field at low temperatures. We also show that the dilution of the complex in the diamagnetic matrix can further improve the dynamic relaxation properties of this system by several orders of magnitude. In conclusion, we have leveraged the design principles for known late lanthanide sandwich complexes to synthesize a zero-field SMM based on a more natural abundant early lanthanide, Nd. The use of bulky (Cpttt)- ligands enables to tailor the coordination environment and to mitigate the fast relaxation of the magnetic moment.

Can early lanthanide sandwich complexes be high performing single-molecule magnets?

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.