Competition Between Intermolecular Interactions in the Self-Assembly of Cocrystals of Polyfluorinated Arylenediamines with Crown Ethers: Effect of the Cyano Group

Abstract

2,4-Diamino-3,5,6-trifluorobenzonitrile makes cocrystals with macrocyclic 18-crown-6, 15-crown-5, and 12-crown-4 ethers of 4:3, 1:1, and 2:1 stoichiometries respectively. The inability to 1:1 cocrystallization with 18-crown-6 and a nonmonotonic change in the diamine fraction in the cocrystal when the macrocycle size changes distinguish it from a series of structurally similar polyfluoroarylenediamines. In all cocrystals synthesized the cyano group and the polyfluoroaromatic moiety participate in structure-forming interactions (N–H⋯N_cyano H-bond, π⋯π and p⋯π contacts) supplementing the N–H⋯O_cr H-bond with crown ether. Quantum chemical DFT computations of the molecular electrostatic potential, binding energies, and topological parameters of the electron density in dimers show a considerable contribution of interactions between aromatic coformer molecules to stabilization of the cocrystal structure. The key factor providing the 1:1 cocrystallization is π-stacking occurring in the cocrystal with 15-crown-5 and is violated when passing to 18-crown-6 due to an increase in the macrocycle size. The structural and quantum chemical analysis performed characterizes the hierarchy of supramolecular synthons as tools to design molecular crystals.