Add time:07/23/2019         Source:sciencedirect.com

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, CF3). 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 CF3-containing polyfluorophenylenediamines are 2D assemblies connected via synthon Сar–N–H … Ocr. 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 Сar–N–H … Npy, 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 |ΔΔHsubl| 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.

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