Host behaviour of 1,2-DAX, 1,2-DAT, 1,4-DAX and 1,4-DAT in mixtures of methyl-, ethyl- and isopropyl-substituted aromatic guest compounds

In this work, the host ability of four compounds based on the xanthenyl- and thioxanthenyl-fused tricyclic systems, trans‑N,N′‑bis(9‑phenyl‑9‑xanthenyl)cyclohexane‑1,2‑diamine (1,2-DAX), trans‑N,N′‑bis(9‑phenyl‑9‑thioxan-thenyl)cyclohexane‑1,2‑diamine (1,2-DAT), trans‑N,N′‑bis(9‑phenyl‑9‑xanthenyl)-cyclohexane‑1,4‑diamine (1,4-DAX) and trans‑N,N′‑bis(9‑phenyl‑9‑thioxanthenyl)cyclohexane‑1,4‑diamine (1,4-DAT), were assessed and compared when presented with three alkylaromatic systems, namely toluene (TOL), ethylbenzene (EB) and cumene (CUM). When these host compounds were recrystallized from each guest solvent, complexes formed in each instance, with the exception of experiments involving CUM and the 1,4 host analogues, where inclusion did not take place. Guest/guest competition experiments revealed that the 1,2 host analogues were significantly less selective in their behaviours compared with their 1,4 host analogues, with only marginal preferences noted for CUM and TOL in the case of 1,2-DAX and 1,2-DAT, respectively. Selectivities ranged between 49.1‒65.1 and 50.9‒74.8% for each of these 1,2 analogues, while these were between 56.6‒93.9 and 61.2‒85.8% for 1,4-DAX and 1,4-DAT. 1,4-DAX performed optimally in two binary mixtures, where the preference for TOL was 93.9% and for EB 91.3% when the other guest was CUM. The host···guest interactions responsible for guest retention were investigated by means of single crystal diffraction analyses, and the relative thermal stabilities of the crystalline complexes using thermoanalytical experiments. More usually, these techniques explained the preferential behaviour noted for these host compounds in the competition experiments.