The proton-transfer compounds of strychnine with achiral salicylic acids : strychninium 3,5-dinitrosalicylate and the strychninium 5-nitrosalicylate bis(5-nitrosalicylic acid) adduct

In the crystal structures of the proton-transfer compounds of strychnine with 3,5-dinitrosalicylic acid, namely strychninium 3,5-dinitrosalicylate, C21H23N2O2+.C7H3N2O7-, (I), and 5-nitrosalicylic acid, namely strychninium-5-nitrosalicylate-5-nitrosalicylic acid (1/1/2), C21H23N2O2+.C7H4NO5-.2C7H5NO5, (II), protonation of one of the N atoms of the strychnine molecule occurs and this group is subsequently involved in intermolecular hydrogen-bonding interactions. In (I), this is four-centred, the primary being with an adjacent strychninium carbonyl O-atom acceptor in a side-to-side interaction giving linear chains. Other interactions are with the phenolate and nitro O-atom acceptors of the anionic species, resulting in a one-dimensional polymer structure. In (II), the N+-H interaction is three-centred, the hydrogen bonding involving carboxyl O-atom acceptors of the anion and both acid adduct species, giving unique discrete hetero-tetramer units. The structure of (II) also features pi-bonding interactions between the two acid adduct molecules.