Crystal structure of β-cyclodextrin-4-chlorobenzoic acid complex: unusual C–Cl⋯π interaction between 4-chlorobenzoic acids in β-cyclodextrin dimer

The inclusion complex of β-cyclodextrin (β-CD) with 4-chlorobenzoic acid was synthesized and its crystal structure was determined by single crystal X-ray diffraction under cryogenic condition. The complex contains two β-CDs, two 4-chlorobenzoic acids and twenty-nine water molecules in the asymmetric unit, and can be formulated as 2(C42H70O35)·2(C7H5O2Cl)·29(H2O). In the crystal lattice, two β-CDs form a face-to-face dimer jointed together through hydrogen bonding between the secondary hydroxyl groups of β-CDs. Two 4-chlorobenzoic acid molecules which contact by C–Cl⋯π interactions are included in the β-CD dimer cavity. The β-CD dimers are arranged in brickwork-like pattern along the crystallographic a-axis. The effect of guest molecule length on the inclusion geometry was discussed by comparative study of some β-CD complexes containing similar guests.