Design and supramolecular structure of crystal associates of polyfluoroarylenediamines and 18-crown-6 (2:1)

Abstract The possibility of co-crystallization of polyfluoroaromatic meta -diamines with 18-crown-6 in the 2:1 ratio was tested using a large group of substrates with various frameworks (benzene, naphthalene, and pyridine) and substituents (H, Cl, CF 3 ). Co-crystals of 2:1 stoichiometry were obtained from hexafluoro-2,7-naphthylenediamine, 4-trifluoromethyltrifluoro- and 2-trifluoromethyl-4,6-difluro-1,3-phenylenediamines, 4-chlorodifluoro-2,6-diaminopyridine. According to X-ray crystallographic data, associates of CF 3 -containing polyfluorophenylenediamines are 2D assemblies connected via synthon С ar – N–H … O cr . Polyfluorinated 2,7-diaminonaphthalene and 2,6-diamino-4-chloropyridine form 1D assemblies, in which the π-stacking of the naphthylenediamine molecules and the hydrogen bond С ar – N–H … N py , respectively, are the additional structure-supporting interactions. The co-crystallization of 18-crown-6 with less electron withdrawing arylenediamines gives only associates of stoichiometry 1:1 irrespective of the components ratio and the solvent nature. To rationalize the different co-crystallization behavior of the arylenediamines, the co-crystal structures were studied using a special version of the DFT, which accounts for the van der Waals interactions. The calculated difference between the specific sublimation enthalpies for the 1:1 and 2:1 associates was suggested to be a measure of the preferable co-crystallization ratio: the both types of associates are formed when |ΔΔ H subl | is smaller than 15 J g −1 , a higher value indicates a significant energy preference for one of the structures. The experimental melting enthalpy values (DSC data) for the 1:1 and 2:1 co-crystals based on the same diamine are quite similar.