Comparing the effect of selected substituent changes on host ability and selectivity in four xanthenyl-type host compounds in the presence of cyclohexanone and methylcyclohexanone isomers

Four related xanthenyl and thioxanthenyl host compounds, N,N′-bis(9-phenyl-9-thioxanthenyl)ethylenediamine (H1), N,N′-bis(9-phenyl-9-xanthenyl)ethylenediamine (H2), N,N′-bis(9-cyclohexyl-9-thioxanthenyl)ethylenediamine (H3) and N,N′-bis(9-cyclohexyl-9-xanthenyl)ethylenediamine (H4) were synthesized and compared for their host ability and selectivity in the presence of cyclohexanone and the methylcyclohexanone isomers. Surprisingly, only H1 was an effective host compound in these conditions, clathrating all four potential guest solvents; H2 failed to crystallize from these compounds, while both H3 and H4 included only cyclohexanone, also failing to crystallize from the methylcyclohexanone isomers. H1 was further assessed for any selectivity when presented with mixtures of these guests, and a host selectivity order of 2MeCy (67.6%) > 3MeCy (23.1%) > 4MeCy (9.3%) was observed, while the addition of cyclohexanone to these experiments resulted in an adaptation of this order [Cy (39.2%) = 2MeCy (41.7%) ≫ 3MeCy (13.5%) > 4MeCy (5.6%)]. SCXRD analysis demonstrated that the host packing in H1·Cy, H1·2MeCy and H1·3MeCy was isostructural (monoclinic, P21/n), while H1·4MeCy crystallized in a different crystal system (triclinic, P − 1). All four guests experienced (host)C–H···O–C(guest) interactions, with Cy, a preferred guest, experiencing the shortest of these (2.40 A, 167°). Thermal analyses showed the preferred guests (cyclohexanone and 2-methylcyclohexanone) to form complexes with enhanced thermal stabilities relative to the other two (3- and 4-methylcyclohexanone) (Tp 129.8 and 99.0 °C vs. 97.9 and 95.3 °C, respectively). This investigation has demonstrated that subtle changes in the structures of these xanthenyl- and thioxanthenyl-type host systems may instigate dramatic host behaviour changes in the presence of these cyclohexanone guest solvents.