Role of structural dimensionality in the magneto-chiral dichroism of chiral molecular ferrimagnets

Abstract

Here we report on magneto-chiral dichroism (MChD) detected with visible light on the chiral molecular ferrimagnet [{Cr^III(CN)₆}(Mn^IINH₂ala)₃]·3H₂O (X = S, R; NH₂ala = 2-aminoalanine). Single crystals suitable for magneto-chiral optical measurements were grown starting from enantiopure precursors. X-ray diffraction and magnetic measurements confirmed the 3D-helical structure of the material, its absolute configuration, and its ferrimagnetic ordering below 35 K. Absorption and MChD spectra were measured between 520 and 900 nm from room temperature down to 4 K. At 4 K the electronic spectrum features spin-allowed and spin-forbidden transitions of Cr^III centers and metal-to-metal charge transfer bands. The MChD spectra below the magnetic ordering temperature exhibit absolute configuration-dependent MChD signals, whose shape and intensity closely resamble that of a recently investigated 2D-layered chiral ferrimagnet featuring the same building blocks but different chiral ligands and a lower structural dimensionality. By comparing the temperature and magnetic field dependence of the MChD signals in these two chiral molecular ferrimagnets, we unravel the effect of structural dimensionality in MChD and provide chemical design criteria towards highly responsive magneto-chiral optical materials.