Investigation of the hydrogen bonded host‧‧‧guest and guest‧‧‧guest interactions present in complexes of a polyaromatic wheel-and-axle host compound with dioxane, morpholine, piperidine and pyridine

1,4-Bis(diphenylhydroxymethyl)benzene (H), a host compound possessing wheel-and-axle geometry, was found to possess host ability for dioxane (DIO), morpholine (MOR) and piperidine (PIP), forming inclusion compounds with each one with 1:2 host:guest ratios. This observation prompted an investigation of the host behaviour in mixtures of these guest compounds but where pyridine (PYR) was also considered (PYR was reported earlier to also form a 1:2 complex with H). In mixtures, H demonstrated significant affinities for, more especially, MOR and PIP, while DIO and PYR were usually disfavoured guest species. Single crystal X-ray diffraction experiments revealed that MOR (a favoured guest species) interacted by means of three hydrogen bonds with both adjacent guest and host molecules, plausibly explaining the host preference for this guest species; each of DIO, PYR and PIP were involved in only one interaction of this type with H. Total energy calculations revealed that the host-guest molecular pairs involving preferred MOR and PIP possessed significantly lower energies than those with disfavoured DIO and PYR. Thermal analyses demonstrated that the complex containing the least favoured guest compound, H‧2(DIO), possessed the lowest thermal stability of the four complexes, but these experiments did not clearly explain the affinity of H for MOR.