Crown Ether-Promoted Helical Self-Assembly of Achiral Molecules: Symmetry Breaking in Cocrystallization of Octafluorobenzidine with 18-Crown-6.

New H-bonded supramolecular assembliesare obtained using the polyfluorobiphenyl H-donor derivatives and 18-crown-6 ether. Cocrystals of octafluorobenzidine with 18-crown-6 of 1:1 stoichiometry belong to the enantiomorphous space groups P6₅ and P6₁. The helical self-assembly of these achiral molecules is achieved due to the interplanar angle of the bis-aryl molecule (≈60°), which is fixed by directed N-H···O_cr H-bonds between two H_amino atoms with two O_cr atoms at both ends of the molecule. Cocrystallization of octafluorobiphenol results in the formation of a crystalline hydrate based on the water-mediated H-bond Ar-O-H···O(H)-H···O_cr. Flexible water linker eliminates the effect of the H-donor coformer structure and makes this cocrystal achiral. The hydrogen bonding details between octafluorobenzidine and 18-crown-6 within a unit cell are investigated through a combination of vibrational spectroscopy and quantum mechanical calculations. An oxygen atom in 18-crown-6 is identified as a chiral center, as a result of intermolecular interactions involving this atom and hydrogen atoms bonded to its α and β carbon atoms. The unique interaction patterns of 18-crown-6 with acetone and chloroform, along with scanning electron microscopic images, reveal the role of solvent molecules in determining the chirality of the self-assembly.