Molecular structures of the inclusion complexes β-cyclodextrin–1,2-bis(4-aminophenyl)ethane and β-cyclodextrin–4,4′-diaminobiphenyl; packing of dimeric β-cyclodextrin inclusion complexes

Abstract

The present investigation is part of an ongoing study on the influence of the long end-functonalized guest molecules DBA and BNZ in the crystal packing of β-cyclodextrin (βCD) dimeric complexes. The title compounds are 2:2 host:guest complexes showing limited host–guest hydrogen bonding at the primary faces of the βCD dimers. Within the βCD cavity the guests exhibit mutual π...π interactions and between βCD dimers perpendicular NH...π interactions. The DBA guest molecule exhibits one extended and two bent conformations in the complex. The BNZ guest molecule is not planar inside βCD, in contrast to the structure of BNZ itself, which indicates that the cavity isolates the molecules and forbids the π...π stacking of the aromatic rings. NMR spectroscopy studies show that in aqueous solution both DBA and BNZ form strong complexes that have 1:1 stoichiometry and structures similar to the solid state ones. The relative packing of the dimers is the same in both complexes. The axes of two adjacent dimers form an angle close to 20° and have a lateral displacement ≃2.45 Å, both of which characterize the screw-channel mode of packing. Although the βCD/BNZ complex indeed crystallizes in a space group characterizing the latter mode, the βCD/DBA complex crystallizes in a space group with novel dimensions not resembling any of the packing modes reported so far. The new lattice is attributed to the three conformations exhibited by the guest in the crystals. However, this lattice can be transformed into another, which is isostructural to that of the βCD/BNZ inclusion complex, if the conformation of the guest is not taken into account.