Hydrogen bonding isosteres: bimolecular carboxylic acid and amine-N-oxide interactions mediated via CH...O hydrogen bonds.

Abstract The X-ray structures of cocrystals between 2,2′-dipyridyl- N , N ′-dioxide ( 1 ) with fumaric acid ( 2 ), itaconic acid ( 3 ), succinic acid ( 4 ), and oxalic acid ( 5 ) were solved to determine if concurrent CH···O interactions were capable of orienting the bimolecular association of the two molecules. Cocrystals 1·2 , 1·3 and 1·4 produce cyclic hydrogen bonded motifs employing pair-wise OH···O and CH···O hydrogen bonds, whereas cocrystal 1·5 forms analogous OH···O hydrogen bonds with a different set of intermolecular CH···O hydrogen bonds. Evidence of cocrystal formation was also observed for these complexes by differential scanning calorimetry and FT-IR spectroscopy. The structures of 1·2 , 1·3 and 1·4 demonstrate the potential of the pair-wise OH···O and CH···O hydrogen bonding interactions and serve to illustrate their use as hydrogen bonding isosteres in crystal engineering, molecular recognition, and drug design.