Complementary Host Behavior of Fluorenone-Derived Host Compounds during Crystallization Processes from Mixed Anilines

Two fluorenone-derived compounds, namely 9,9′-(1,4-phenylene)bis(fluoren-9-ol) (H1) and 9,9′-(ethyne-1,2-diyl)bis(fluoren-9-ol) (H2), were examined for their host behavior in potential guest solvents aniline, N-methylaniline and N,N′-dimethylaniline (ANI, NMA and DMA). Single solvent crystallization experiments demonstrated that H1 formed complexes with ANI (host/guest ratio 1:1) and DMA (1:2), while H2 included all three solvents, ANI (1:2), NMA (1:1) and DMA (2:1). Single crystal X-ray diffraction analyses showed that all complexes were stabilized by means of classical (host)O–H···N(guest) hydrogen bonds in addition to other short contacts. Equimolar binary guest competition experiments with H1 revealed an extremely high host selectivity for DMA (ANI/DMA and DMA/NMA experiments furnished crystals with >91% DMA), while the experiment with all three anilines present also resulted in a complex with an overwhelming amount of DMA (88.3%). H2, on the other hand, selected ANI preferentially in equimolar ANI/NMA and ANI/DMA solutions (93.5 and 66.1% ANI), while the ternary guest experiment also showed an increased affinity for ANI (72.4%). In binary guest competition experiments in which the guest concentrations were varied, H1 displayed, once more, significant selectivities toward DMA (and ANI in its absence), and the selectivity coefficients (K) calculated were oftentimes >10, implying that separations of many of these mixtures are feasible on a practical platform using supramolecular chemistry strategies. Furthermore, H2 demonstrated an ability to extract large amounts of ANI from 80:20 ANI/NMA, and 60:40 and 80:20 ANI/DMA mixtures. Both thermal and Hirshfield surface analyses were, moreover, carried out on the complexes produced in this work.