Construction of Chiral Polar Crystals from Achiral Molecules by Stacking Control of Hydrogen-Bonded Layers Using Type II Halogen Bonds

Crystals belonging to P1 and P21 space groups are fascinating research targets because of their potential applications in various fields by taking advantage of their chirality and polarity. However, molecules intrinsically prefer symmetric, achiral nonpolar space groups due to canceling out of dipole moments and close packing in crystalline states. Therefore, it remains difficult to selectively obtain the P1 and P21 crystals, especially from achiral molecules. Here we achieve construction of the chiral P1 and P21 crystals from achiral molecules based on stacking control of chiral two-dimensional hydrogen-bonded layers by halogen bonds (XBs). Precise investigations and theoretical calculations of their crystal structures revealed that space group selectivity among the chiral P1, P21, and achiral space groups is the result of a subtle balance between the stronger interaction: charge-assisted hydrogen bonds and the weaker interactions: van der Waals interaction of alkyl chains and the bonding involving halog...