The host behaviour of 9-phenyl-9 H-xanthene derivatives in mixtures of cyclohexanone and the methylcyclohexanone isomers

Abstract

Here we report on the host behaviour of compounds N, N’-bis(9-phenyl-9-xanthenyl)propane-1,3-diamine (H1) and N, N’-bis(9-phenyl-9-xanthenyl)butane-1,4-diamine (H2) in the presence of potential guest species cyclohexanone (CYC) and 2-, 3- and 4-methylcyclohexanone (2MeCYC, 3MeCYC and 4MeCYC). H1 only formed a complex with CYC, whilst all four guest solvents were enclathrated by H2. Thermal analyses in conjunction with SCXRD experiments revealed that more energy was required to remove guest species from the crystals of their complexes when they were housed in discrete cavities compared with guest molecules retained in channels. Only in H1·CYC was identified an intramolecular (host)N‒H···N(host) hydrogen bond, while complexes H2·2(CYC), H2·2(3MeCYC) and H2·4MeCYC all experienced strong (host)N‒H···O(guest) hydrogen bonds which assisted in retention of the guests in the complexes; this interaction type was absent in both H1·CYC and H2·2(2MeCYC). Hirshfeld surface analyses demonstrated that the amounts of (guest)O···H(host) interatomic interactions were comparable and ranged between 11.1 and 13.9%. Guest competition experiments showed that H2 possessed an affinity for, more usually, 3MeCYC, despite the complex H2·2(3MeCYC) being the least thermally stable one. Finally, it was established that H1 and H2 would not be appropriate host compounds for separations of mixed cyclohexanones through supramolecular chemistry strategies.