Magnetooptical Properties of Chiral [Co2Ln] Clusters

Two pairs of enantiomeric 3d-4f metal clusters, [Co2Ln[(R)/(S)-L]4]·Cl5·(H2O)2·CH3OH·CH3CH2OH [Co2Ln; Ln = Gd (1S and 1R), Dy (2S and 2R)], were synthesized by the reaction of chiral Schiff-base ligand (R)/(S)-3-[(2-hydroxybenzylidene) amino]propane-1,2-diol [(R)/(S)-HL] with CoCl2·6H2O and LnCl3·6H2O. The circular dichroism spectra of (S)/(R)-Co2Ln display a mirror-symmetry effect with seven peaks at 210-800 nm, which can be ascribed to π-π* transitions, exciton coupling, charge-transfer transitions between ligands and Co3+, and characteristic d-d transitions of Co3+ ions. Interestingly, the chiral Co2Ln metal clusters display strong magnetic circular dichroism signals at room temperature. This work suggests that the chiromagnetic metal cluster is expected to show a strong magnetooptical response.