Molecular clips form isostructural dimeric aggregates from benzene to water

We report the synthesis and characterization of eight C-shaped methylene-bridged glycoluril dimers (1-8) bearing hydrogen-bonding amide groups on their aromatic rings. Compounds 1-6 undergo tight dimerization in CDCl3 solution (K-s > 9 x 10(5) M-1); binary mixtures of 1-7 form mixtures of homodimers and heterodimers in moderately selective dimerization processes (0.23 less than or equal to K-eq less than or equal to 768; 0.253 less than or equal to chi(AB) < 0.933). The high affinity formation of 1(.)1-6(.)6 is due to the commensurate nature of the geometrical constraints imposed by the pi-pi interactions and only two hydrogen bonds. The differential response of the strengths of the pi-pi interactions and H-bonds of 2(.)2 to changes in solvent polarity-from C6D6 to D2O-results in the formation of a solvent-independent isostructural aggregate that exhibits high affinity dimerization across the full range of solvents.