Ligand Fluorination to Mitigate the Raman Relaxation of DyIII Single‐Molecule Magnets: A Combined Terahertz, Far‐IR and Vibronic Barrier Model Study.

The fast Raman relaxation process via a virtual energy level has become a puzzle for how to chemically engineer single‐molecule magnets (SMMs) with better performance. Here, we use the trifluoromethyl group to systematically substitute the methyl groups in the axial position of the parent bis‐butoxide pentapyridyl dysprosium(III) SMM. The resulting complexes—[Dy(OLA)2py5][BPh4] (LA=CH(CF3)2−1, CH2CF3−2, CMe2CF3−3)—show progressively enhanced TBhys (@100 Oe s−1) from 17 K (for 3), 20 K (for 2) to 23 K (for 1). By experimentally identifying the varied under barrier relaxation energy in the 5–500 cm−1 regime, we are able to identify that the C−F bond related vibration energy of the axial ligand ranging from 200 to 350 cm−1 is the key variant for this improvement. Thus, this finding not only reveals a correlation between the structure and the Raman process but also provides a paradigm for how to apply the vibronic barrier model to analyze multi‐phonon relaxation processes in lanthanide SMMs. [ABSTRACT FROM AUTHOR]