9,9'-Bifluorenyl-9,9'-diol as an effective purification tool for N-methyl- and N,N-dimethylaniline mixtures through...

This study employed 9,9'-bifluorenyl-9,9'-diol (H) as a host compound for the separation of mixed anilines through host-guest chemistry strategies. H successfully enclathrated aniline (ANIL), N-methylaniline (NMA) and N,N-dimethylaniline (DMA) with 1 : 1, 1 : 1 and 3 : 2 H : G ratios, respectively, when it was crystallized independently from each of these guest solvents. In the equimolar guest competition experiments, H preferentially included NMA, followed by ANIL, while DMA was consistently disfavoured. The binary guest competition experiments demonstrated that H possesses the ability to separate all NMA/DMA solutions (favouring NMA), since significant host selectivities were observed in these experiments. SCXRD analyses showed that the preferred guest, NMA, in its complex with H, experienced both classical and non-classical hydrogen bonding with the host molecule, while ANIL (second preferred), in the H·ANIL complex, engaged only in classical hydrogen bonds with H; DMA (least favoured) in 3(H)·2(DMA), on the other hand, did not experience significant hydrogen bonding with the host molecule. Moreover, it was also noted that the H·NMA complex possessed the highest crystal density of the three inclusion compounds, reflecting a denser packing and a greater thermodynamic stability compared with the ANIL- and DMA-containing complexes. Hirshfeld surface analyses revealed that the three-dimensional surfaces surrounding the ANIL and NMA guest molecules had pronounced red regions, consistent with the hydrogen bonding observed in their crystal structures, while the surface around DMA showed only a small red area, reflecting the absence of any significant hydrogen bonding. Finally, thermal experiments confirmed that, of the three complexes, H·NMA possessed the highest thermal stability, followed by H·ANIL, while 3(H)·2(DMA) was least stable, in accordance with the host selectivity behaviour in guest mixtures. In summary, this investigation demonstrated that H has exceptional separation potential for all NMA/DMA mixtures when employing a host-guest chemistry approach.