Rebek's Diacid-Pyrazine Complex

This is the crystal structure of a hydrogen-bonded complex of the so-called "Rebek's diacid" (a molecular host with convergent carboxyl groups) with the small diamine pyrazine. The structures of this and related complexes had been controversial. Rebek originally proposed that two hydrogen bonds are formed in the complex; later calculations by Jorgensen suggested that only one could be made. The X-ray structures of the complexes support the original formulation of Rebek. For a brief communication describing the first X-ray structure of one of these complexes, see "Molecular Structure of Rebek's Diacid-Quinoxaline: Confirmation of Two-Point Binding." R. A. Pascal, Jr., and D. M. Ho, J. Am. Chem. Soc. 1993, 115, 8507-8508.