Crystal structure of β-cyclodextrin-benzoic acid inclusion complex

The inclusion complex of beta-cyclodextrin (beta-CD) with benzoic acid (BA) has been characterized crystallographically. Two beta-CDs cocrystallize with two BAs, 0.7 ethanol and 20.65 water molecules [2(C6H10O5)(7).2(C7H6O2).0.7(C2H6O).20.65H(2)O] in the triclinic space group P1 with unit cell constants: a = 15.210(1), b = 15.678(1), c = 15.687(1) Angstrom, alpha = 89.13(1), beta = 74.64(1), gamma = 76.40(1)degrees. The anisotropic refinement of 1840 atomic parameters against 16,201 X-ray diffraction data converged at R = 0.078. In the crystal lattice, beta-CD forms dimers stabilized by direct O-2(m)_1/O-3(m)_1(...)O-2(n)_2/O-3(n)_2 hydrogen bonds (intradimer) and by indirect O-6(m)_1(...) O-6(n)_2 hydrogen bonds with one or two bridging water molecules joined in between (interdimer). These dimers are stacked like coins in a roll constructing endless channels where the guest molecules are included. The BA molecules protrude with their COOH groups at the beta-CD O-6-sides and are maintained in positions by hydrogen bonding to the surrounding O-6-H groups and water molecules. Water molecules (20.65) are distributed over 30 positions in the interstices between beta-CD molecules, except the water sites W-1, W-2 that are located in the channel of the beta-CD dimer. Water site W-2 is hydrogen bonded to the disordered ethanol molecule (occupancy 0.7). (C) 2003 Elsevier Science Ltd. All rights reserved.