The behaviour of two diamino-derived host compounds in cyclohexanone and isomeric methylcyclohexanones†

The present investigation centred around the host ability of two novel compounds, N,N′-bis(5-phenyl-5-dibenzo[a,d]cycloheptenyl)propane-1,3-diamine (DB3) and N,N′-bis(9-phenyl-9-thioxanthenyl)butane-1,4-diamine (S4), for guest solvents cyclohexanone and its methylcyclohexanone isomers (Cyc, 2MeCyc, 3MeCyc and 4MeCyc). While DB3 formed complexes with each of these organic solvents, S4 only included 4MeCyc. All complexes were characterized by 1 : 1 host : guest ratios. With the view to assessing whether these host compounds have the potential to separate mixtures of the cyclohexanones, each one was crystallized from various guest mixtures. It was determined that such separations would not be feasible through supramolecular chemistry strategies with these two host species owing to low calculated selectivity coefficients (K). This was despite the observed selectivity of DB3 for 4MeCYC and Cyc in the mixed guest experiments. However, a thorough scrutiny of the five novel complexes was subsequently undertaken, and the crystal structures, through SCXRD analysis, demonstrated that Cyc, a preferred guest solvent, when included by DB3, occupied highly constricted channels, while these were comparatively wider and more open in the complexes with the MeCycs. Furthermore, preferred Cyc was the only guest molecule that engaged in a classical hydrogen bond with DB3, and Hirshfeld surface analyses showed this guest (which only has 10 hydrogen atoms) to be involved in the greater quantity of (guest)H⋯H(host) interactions (the MeCyc molecules have 12 hydrogen atoms and experienced less of this type of interaction). All of these observations provide an explanation for the affinity of DB3 for Cyc (but not for 4MeCyc). These SCXRD analyses further demonstrated that the geometry of the diamino linker in the DB3 complexes was more folded in nature while, in S4·4MeCyc, this was in an extended zig-zag orientation. Finally, thermal analyses on each of the complexes, unsurprisingly, demonstrated the Cyc-containing complex with DB3 to be the most stable one.