Host behaviour of two tricyclic fused systems in mixed anisole guest solvents

Abstract

Two tricyclic fused host systems, namely N,N′-bis(5-phenyl-5-dibenzo[a,d]cycloheptenyl)ethylenediamine H1 and N,N′-bis(5-phenyl-10,11-dihydro-5-dibenzo[a,d]cycloheptenyl)ethylenediamine H2, were recrystallized from each of anisole and 2-, 3- and 4-methylanisole (ANI, 2MA, 3MA and 4MA), and it was observed that H1 formed complexes with 2MA (host : guest 2 : 1), 3MA (1 : 1 at 4 °C) and 4MA (1 : 1), while H2 only enclathrated ANI (2 : 3). Mixed solvent competition experiments using H1 revealed this host compound to possess a remarkable affinity for 4MA; in fact, complexation was only successful if this guest compound was present in the mixture. Similar experiments but with H2 were, unfortunately, not enlightening owing to the fact that crystals did not form in these conditions. SCXRD experiments showed that the affinity of H1 for 4MA relative to 3MA was as a result of intermolecular host⋯host C–H⋯π and π⋯π interactions in H1·4MA that were significantly shorter than in H1·3MA which, in turn, led to a higher crystal density for H1·4MA (1.215 g cm⁻¹) compared with H1·3MA (1.184 g cm⁻¹), despite their identical chemical formulae. Thermal analyses showed that the guest molecules in H1·4MA also escaped from the crystals at a higher temperature (104.9 °C) than that in H1·3MA (70.5 °C). Unfortunately, from selectivity coefficient (K) calculations, H1 would not be able to serve as an ideal host candidate for the separations of these anisole mixtures.