Evaluating the host potential of 9,9’-bifluorenyl-9,9’-diol for anisole and the three methylanisole isomers, and its behaviour in mixed guest solutions

In the present investigation, 9,9’-bifluorenyl-9,9’-diol ( H ) was assessed for its host potential for anisole (ANI) and the three methylanisole isomers (2MA, 3MA and 4MA), through crystallization experiments, and it was thus demonstrated that H has the ability to enclathrate each of these four guest solvents. Additionally, the selectivity behaviour of H was evaluated when presented with mixtures of these anisoles, and the results suggested that each of the methylated anisoles was preferred in one or another instance, dependent upon the other guest solvent/s present, while, more notably, ANI remained consistently disfavoured. However, the observed host selectivity was not appropriate to suggest that H may serve as a host candidate for the separation of ANI/MA solutions through host‒guest chemistry protocols. Single crystal X-ray diffractometric analyses on each of the complexes produced in this work showed that, with the exception of H ·0.75(4MA 2 ), extreme guest disorder and/or severe twinning of the crystals existed, and Platon’s SQUEEZE routine was required in most instances. As such, these experiments did not provide explanations for the selectivity behaviour of the host compound in the mixed guest solutions through a consideration of the host···guest interactions present in each complex. However, from the successful obtention of the crystal structure of H ·0.75(4MA 2 ), it was observed that the guest species was retained in the crystals of the complex by means of both (host)O–H···O(guest) and (host/guest)C–H···C–C(guest/host) close contacts. Thermal analysis demonstrated that, while the ANI, 2MA and 3MA inclusion complexes were unstable at ambient conditions, the two 4MA-containing inclusion compounds possessed stability, and comparably so, since similar guest release onset temperatures for their guest release events were observed (T on , 65.9 and 68.8 °C). These observations provide some explanation for the preference of H for 4MA in a number of the guest competition experiments, more especially those that were equimolar and binary in nature.