Crystal structures of two forms of a 2:1 cyclomaltohexaose (α-cyclodextrin)/4,4′-biphenyldicarboxylic acid inclusion complex

The inclusion complex of cyclomaltohexaose (alpha-cyclodextrin, alpha-CD)/4,4'-biphenyldicarboxylic acid (BPDC) was crystallized into two crystal forms, tetragonal, space group P4(2)2(1)2, a=b=19.609(8) Angstrom, c=32.257(8) Angstrom (Form 1), and orthorhombic, space group P2(1)2(1)2, a = 35.397(8) Angstrom, b = 24.577(5) Angstrom, c = 27.969(9) Angstrom (Form 2). Both crystal structures were determined by the X-ray diffraction method. The results show that a guest BPDC was included in two alpha-CDs in the tail-to-tail orientation to form the 2:1 alpha-CD/BPDC inclusion complex, and that a BPDC interacts with another BPDC by guest-water-guest hydrogen bonds. In Form 1, the alpha-CDs are arranged in a continuous one-dimensional column structure, whereas in Form 2 they are arranged in a discontinuous array. (C) 1998 Elsevier Science Ltd. All rights reserved.