Magneto-Chiral Dichroism of Tris-Chelated Cr(III) Complexes for Magneto-Chiral Photochemistry Studies

Here we report on the preparation and investigation of a pair of enantiopure chiral complexes of chromium(III) featuring the chiral (1R,2R)-diaminocyclohexane and (1S,2S)-diaminocyclohexane ligands. Single-crystal X-ray crystallography reveals an octahedral tris-chelated propeller-like coordination geometry. Natural circular dichroism spectroscopy in solution and in the solid state indicates that both spin-allowed and spin-forbidden d–d electronic transitions of the Cr(III) ion are optically active. Variable temperature and variable magnetic field magneto-chiral dichroism spectroscopy reveals that the spin-forbidden absorption bands are MChD active and provide low-temperature g_MChD dissymmetry factors comparable to those of tris(oxalato)chromate(III). On these bases, magneto-chiral photochemistry experiments aimed at inducing a preferential enantiomeric excess of one enantiomer over the other by irradiating a racemic solution of the complexes with unpolarized light under an applied magnetic field have been conducted.