5-nitrosalicylic acid and its proton-transfer compounds with aliphatic lewis bases

The crystal structures of the proton-transfer compounds of 5-nitrosalicylic acid (5-nsa) with morpholine (morph), hexamethylenetetraminc (hmt), and ethylenediamine (en) have been determined and their solid-state packing structures described. The compounds are [(morph)⁺(5-nsa) ^-] 1, [(hmt)⁺(5-nsa)^-·H₂O] 2, and [(en)²⁺(5-nsa)^-·H₂O] 3. In all compounds, protonation of the hetero-nitrogen of the Lewis base occurs. With 1, the 5-nsa anions and the morpholine cations lie, respectively, in or across crystallographic mirror planes and are linked within the planes by hydrogen-bonding interactions through the aminium group and the carboxylic and phenolic oxygens of the anionic 5-nsa species giving a two-dimensional sheet polymer. Compound 2 is an unusual structure with the planar 5-nsa anions lying within pseudo minor planes and cyclically linked by duplex water bridges through a single carboxylate oxygen into centrosymmetric dimers. The hmt cation molecules are disordered across the pseudo mirror and are strongly linked by N⁺-H ... O hydrogen bonds only to the water molecules with peripheral weak hmt C-H ... O hydrogen bonds extending the dimer within and between the dimer planes. Compound 3 is a network polymer comprised of the 5-nsa anions, the en dianions, and the water molecule in an extensive hydrogen-bonded structure.