Magnetic 3d–4f Chiral Clusters Showing Multimetal Site Magneto-Chiral Dichroism

Here, we report the molecular self-assembly of hydroxido-bridged {Ln5Ni6} ((Ln3+ = Dy3+, Y3+) metal clusters by the reaction of enantiopure chiral ligands, namely, (R/S)-(2-hydroxy-3-methoxybenzyl)-serine), with NiII and LnIII precursors. Single-crystal diffraction analysis reveals that these compounds are isostructural sandwich-like 3d–4f heterometallic clusters showing helical chirality. Direct current magnetic measurements on {Dy5Ni6} indicates ferromagnetic coupling between DyIII and NiII centers, whereas those on {Y5Ni6} denote that the NiII centers are antiferromagnetically coupled and/or magnetically anisotropic. Magneto-chiral dichroism (MChD) measurements on {Dy5Ni6} and its comparison to that of {Y5Ni6} provide the first experimental observation of intense multimetal site MChD signals in the visible–near-infrared region. Moreover, the comparison of MChD with natural and magnetic circular dichroism spectra unambiguously demonstrate for the first time that the MChD signals associated with the NiII d–d transitions are mostly driven by natural optical activity and those associated with the DyIII f–f transitions are driven by magnetic optical activity.