Magneto-chiral dichroism of chiral lanthanide complexes in the context of Richardson's theory of optical activity

Here we report on the Magneto-Chiral Dichroism (MChD) detected through visible and near-infrared light absorption of two enantiomeric pairs of Er${}^{III}$ and Tm${}^{III}$ chiral complexes featuring a propeller-like molecular structure. The magnetic properties show typical features of isolated paramagnetic ions associated with ${}^4$I${}_{15/2}$ and ${}^3$H${}_6$ ground state terms. MChD spectroscopy shows high g${}_{MChD}$ dissymmetry factors of ca. 0.12 T${}^{-1}$ and 0.05 T${}^{-1}$ (T=4.0 K and B=1.0 T) for Er${}^{III}$ and Tm${}^{III}$, respectively, associated with the magnetic-dipole allowed ${}^4$I${}_{13/2}$ ← ${}^4$I${}_{15/2}$ and ${}^3$H${}_5$ ← ${}^3$H${}_6$ transitions. MChD signals of the two complexes were detected up to room temperature and under magnetic fields up to 5.0 T. For the first time, the MChD results are discussed in the context of the Richardson theory of lanthanide optical activity and provide clear indications on the strongest MChD-active electronic transitions of lanthanide complexes. (© 2024 Wiley-VCH GmbH)