USE OF HYDROGEN-BONDS TO CONTROL MOLECULAR AGGREGATION - ASSOCIATION OF DIPYRIDONES JOINED BY FLEXIBLE SPACERS

Flexible dipyridone 1, which incorporates an extensive, self-complementary pattern of hydrogen-bond donors and acceptors, exists largely as an antiparallel dimer at 0.0016 M in CHCl3 at 25-degrees-C. In the solid state, however, dipyridone 1 prefers a polymeric motif with an intramolecular hydrogen bond. We propose that the structure formed in solution is dimer 5 joined by four intermolecular hydrogen bonds or dimer 6 held together by two intermolecular hydrogen bonds strengthened by the cooperative effect of two intramolecular hydrogen bonds.