Exploring the hydrogen-bond preference of N-H moieties in co-crystals assembled via O-H(acid)•••N(py) intermolecular interactions

In order to establish the hydrogen-bond preference of an amide based N-H moiety faced with different C=O or -OH hydrogen-bond acceptors, the crystal structures of several new co-crystals and salts were examined: 3-acetaminopyridine fumaric acid (2 : 1) 1, 4-(acetaminomethyl)pyridine fumaric acid (2 : 1) 2, 4-acetaminopyridine decanedioic (sebacic) acid (2 : 1) 3, 4-(acetaminomethyl) pyridine adipic acid ( 2 : 1) 4, 4-( acetaminomethyl) pyridine isophthalic acid (2 : 1) 5, 4-(acetaminomethyl)pyridinium 5-nitro-hydrogen isophthalate hydrate 6, 4-acetaminopyridinium hydrogenglutarate (1 : 1) 7. All co-crystals, 1-5, are constructed from an O-H(acid)N-...(py) hydrogen bond and for the salts, 6-7, the primary synthon is the corresponding charge-assisted N-H+...-O interaction. The remaining N-H donor (on the amide moiety) shows a preference (4 out of 5) for the amide C=O over the acid C=O.