Host-guest supramolecular interactions between a resorcinarene-based cavitand bearing a -COOH moiety and acetic acid

The cavitand 5,11,17,23-tetramethyl-4,24:6,10:12,16:18,22-tetrakis(methylenedi-oxy)resorcin[4]arene functionalized at the upper rim with a carboxylic acid group, CavCOOH-in, of chemical formula C37H32O10, was synthesized in order to study its supramolecular interactions with acetic acid in the solid state. Crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of a dichloromethane-acetone solution of CavCOOH-in, to which glacial acetic acid had been added. The resulting compound, C37H32O10 center dot-2C(2)H(4)O(2) (1) crystallizes in the space group P (1) over bar and its asymmetric unit consists of one molecule of cavitand and two molecules 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 interacts with the host primarily through its methyl group, which (in both orientations) forms C-H center dot center dot center dot pi interactions with the benzene rings of the cavitand. The crystal structure of 1 is dominated by O-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonding due to the presence of acetic acid and of the carboxylic group functionalizing the upper rim. Further stabilization is provided by offset pi-pi stacking interactions between the aromatic walls of adjacent cavitands [intercentroid distance = 3.573 (1) angstrom].