Direct Chiroptical Correlation of Dissymmetric Crystal Morphologies

The link between molecular chirality and crystal shape has been studied since Pasteur correlated macroscopic and microscopic chirality by dissolving dissymmetric tartrate salt crystals and measuring the optical activity of the solutions. 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 are correlated with single crystal optical activity along the accessible low symmetry directions. Moreover, the bipyridimal crystals show unusual dissymmetry between the upper and lower regions. Weak X-ray scattering from small crystals were 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.