Unraveling the Structural and Property Differences between Highly Similar Chiral and Racemic Crystals Composed of Analogous Molecules

Abstract

The structural differences between chiral and racemic crystals of enantiomers have piqued interest, as exemplified by classical Wallach’s rule. However, the mechanical and thermal disparities between these materials have not been thoroughly investigated. This study reports the structural and mechanical differences between chiral and racemic crystals of two analogous molecules. The similarity of molecular and crystal structures between the two analogues was validated through comparison with known chiral–racemic crystal pairs. Young’s moduli of the four crystals revealed larger values for racemic crystals than their chiral counterparts, consistent with the intermolecular interaction energies projected along the loading direction. The thermal response of crystals plays a significant role in their elastic behavior, and the temperature dependence of interaction energies along the [001] direction was found to agree with the temperature dependence of lattice dynamics for all four crystals.

Exploration of elastic moduli of molecular crystals via database screening by pretrained neural network potential

“…Pharmaceuticals consisting of small molecules are molecular crystals for suppressing symptoms of diseases, and elastic properties are also important because they are related to the compressibility when converting powder into tablets. 9,10 Although there have been many reports in which Young's modulus in a specific direction has been measured by nanoindentation or bending tests, 11–13 there have been a limited number of literature reports in which the elastic constant tensor has been experimentally determined. Spackman et al reported that the elastic constant tensors of only 80 crystals have been determined since 1950.…”