Roof-shaped hydroxy hosts: synthesis, complex formation and X-ray crystal structures of inclusion compounds with EtOH, nitroethane and benzene

Abstract

A series of crystalline host molecules 1 and 2a–e, based on a characteristic 9,10-dihydro-9,10-ethanoanthracene rigid framework and appended diarylmethanol clathratogenic groups, has been synthesized and studied with regard to their inclusion behaviour. These hosts form crystalline inclusion compounds with a variety of uncharged organic molecules, ranging from protic dipolar to apolar compounds (183 different species), but show a preference for amines and aromatic hydrocarbons. The bis-methanols are largely superior to the mono-methanols, except for the 4-chlorophenyl substituted methanol, which has proved to have equal efficiency.

The building principles and the mode of complexation of the host compound 2a(trans-α,α,α′,α′-tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol) with ethanol (protic), nitroethane (aprotic polar) and benzene (aprotic apolar) as guests have been investigated by single crystal X-ray diffraction. The conformation of the host molecule observed in the 1 : 2 (host: guest) EtOH complex is different from that in the nitroethane (1 : 1) or benzene (2 : 1) inclusions. The host–guest contact pattern in 2a·EtOH (1 : 2) features a huge 16-membered loop of H-bonds involving four functional OH groups of both host and guest, with one intra-host H-bond for each of the two host molecules of the 2 : 4 (host:guest) aggregate. On the other hand, in the compounds of 2a with the aprotic guest species nitroethane and benzene the host hydroxys are involved in specific intramolecular OH ⋯π-aryl contact, thus yielding true lattice-type inclusions, although with different organizations. Accordingly, in 2a·nitroethane (1 : 1) the polar guest units fill up the voids between the bulky host molecules, while in 2a·benzene (2 : 1) the host molecules are arranged so as to form tunnels in the crystallographic c direction, where the guests are located.