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

Abstract

Abstract 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(C 42 H 70 O 35 )·2(C 7 H 5 O 2 Cl)·29(H 2 O). 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.