A Chiral Prussian Blue Analogue Pushes Magneto-Chiral Dichroism Limits

Here we report on magneto-chiral dichroism (MChD) detected with visible light on the chiral Prussian Blue Analogue [Mn^II(X-pnH)(H₂O)][Cr^III(CN)₆]·H₂O (X = S, R; pn = 1,2-propanediamine). Single crystals suitable for magneto-optical measurements were grown starting from enantiopure chiral ligands. X-ray diffraction and magnetic measurements confirmed the 2D-layered structure of the material, its absolute configuration, and its ferrimagnetic ordered state below a critical temperature T of 38 K. Absorption and MChD spectra were measured between 450 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, spin-forbidden transitions of the Mn^II centers, and metal-to-metal charge transfer bands. The MChD spectra below the magnetic ordering temperature exhibit intense absolute configuration-dependent MChD signals. The temperature dependence of these signals closely follows the material magnetization. Under a magnetic field of 0.46 T, the most intense contribution to MChD represents 2.6% T^-1 of the absorbed intensity, one of the highest values observed to date.