Enhancement of Magneto-Chiral Dichroism Intensity by Chemical Design: The Key Role of Magnetic-Dipole Allowed Transitions

Here we report on the strong magneto-chiral dichroism (MChD) detected through visible and near-infrared light absorption up to 5.0 T on {Er₅Ni₆} metal clusters obtained by reaction of enantiopure chiral ligands and Ni^II and Er^III precursors. Single-crystal diffraction analysis reveals that these compounds are 3d-4f heterometallic clusters, showing helical chirality. MChD spectroscopy reveals a high g_MChD dissymmetry factor of ca. 0.24 T^-1 (T = 4.0 K, B = 1.0 T) for the ⁴I_13/2 ← ⁴I_15/2 magnetic-dipole allowed electronic transition of the Er^III centers. This record value is 1 or 2 orders of magnitude higher than that of the d-d electronic transitions of the Ni^II ions and the others f-f electric-dipole induced transitions of the Er^III centers. These findings clearly show the key role that magnetic-dipole allowed transitions have in the rational design of chiral lanthanide systems showing strong MChD.