Host-guest supra-molecular inter-actions between a resorcinarene-based cavitand bearing a -COOH moiety and acetic acid.

The cavitand 5,11,17,23-tetra-methyl-4,24:6,10:12,16:18,22-tetra-kis-(methyl-enedi-oxy)resorcin[4]arene functionalized at the upper rim with a carb-oxy-lic acid group, , of chemical formula CHO, was synthesized in order to study its supra-molecular inter-actions with acetic acid in the solid state. Crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of a di-chloro-methane-acetone solution of , to which glacial acetic acid had been added. The resulting compound, CHO·2CHO () crystallizes in the space group and its asymmetric unit consists of one mol-ecule of cavitand and two mol-ecules of acetic acid, one of which is encapsulated inside the aromatic cavity and disordered over two positions with a refined occupancy ratio of 0.344 (4):0.656 (4). The guest inter-acts with the host primarily through its methyl group, which (in both orientations) forms C-H⋯π inter-actions with the benzene rings of the cavitand. The crystal structure of is dominated by O-H⋯O and C-H⋯O hydrogen bonding due to the presence of acetic acid and of the carb-oxy-lic group functionalizing the upper rim. Further stabilization is provided by offset π-π stacking inter-actions between the aromatic walls of adjacent cavitands [inter-centroid distance = 3.573 (1) Å].