Crystal structure of a cyclomaltoheptaose-4-hydroxybiphenyl inclusion complex.

The crystal structure of the inclusion complex of cyclomaltoheptaose (β-cyclodextrin) with 4-hydroxybiphenyl was determined by single-crystal X-ray diffraction at 150K. The complex contains two cyclomaltoheptaose molecules, two 4-hydroxybiphenyl molecules, one ethanol molecule and fifteen water molecules in the asymmetric unit, and could be formulated as [2(C42H70O35)·2(C12H10O)·(C2H6O)·15(H2O)]. It crystallized in the triclinic space group P1 with unit cell constants a=15.257(3), b=15.564(3), c=15.592(2)Å, α=104.485(15)°, β=101.066(14)°, γ=104.330(17)°, V=3343.6(10)Å3. In the crystal lattice, two β-cyclodextrins form a head-to-head dimer jointed through hydrogen bonds. Two 4-hydroxybiphenyls were included in the dimer cavity with their hydroxyl groups protruding from two primary hydroxyl sides of the cyclodextrin molecules. The guest 4-hydroxybiphenyl molecules linked into a chain via a combination of an O–H⋯O hydrogen bond and face-to-face π–π stacking of the phenyl rings. The crystal structure supports the calculation results indicating that the 2:2 inclusion complex formed by β-cyclodextrin and 4-hydroxybiphenyl is the energetically favored structure.