Direct chiroptical correlation of dissymmetric crystal morphologies

The expression of molecular dissymmetry in crystal form has been studied since Pasteur correlated macroscopic and microscopic chirality by measuring the optical activity of solutions of enantiomorphous tartrate salt crystals. Here, we show a direct correlation between enantiomorphous metal-organic framework (MOF) crystals and the chirality of the molecular structure. The geometry of the habits is correlated with single-crystal optical activity along the accessible low-symmetry directions. Weak X-ray scattering from small crystals was consistent with a hexagonal, enantiomorphous space group. However, the heterochirality of the mirror image forms could not be established with X-rays, necessitating a different approach. The optical circular birefringence of the enantiomorphs as evidenced by chiroptical imaging with a complete polarimetric microscope, was used to correlate optical and morphological chirality.