Topography of the 1:1 α-cyclodextrin–nitromethane inclusion complex

Dissolution of α-cyclodextrin (α-CD) in 9:1 water–nitromethane smoothly generates the title compound, which crystallizes as the pentahydrate in the orthorhombic space group P212121 with a=9.452(4), b=14.299(3), c=37.380(10) Å, and Z=4. Its crystal structure analysis revealed the α-CD macrocycle in an unstrained conformation stabilized through a ring of O-2⋯O-3′ hydrogen bonds between five of the six adjacent glucose residues. The nitromethane is located in the α-CD cavity in an orientation parallel to the plane of the macrocycle, and assumes two sites of equal population with the nitro group in excessive thermal motion; the guest is held by van der Waals contacts and C-H⋯O-type hydrogen bonds to the pyranose H-3 and H-5 protons. The packing of the macrocycles in the crystal lattice is of cage herringbone-type with an extensive intra- and intermolecular hydrogen bonding network. The ready formation of a nitromethane inclusion complex in aqueous nitromethane, and the subtleties of its molecular structure amply demonstrate the ease with which water is expelled from the α-CD cavity by a more hydrophobic co-solvent.