2,6-Dinitrobenzoic acid and its 2 : 1 salts formed with isomeric n-({[(pyridin-1-ium-n-ylmethyl)carbamoyl]formamido}methyl) pyridin-1-ium, n = 2, 3 and 4

Abstract

The co-crystallisation of two equivalents of 2,6-dinitrobenzoic acid (1) with one equivalent of a member of the isomeric N,N′-bis(pyridin-n-ylmethyl)ethanediamides, n = 2, 3 and 4, resulted in the anticipated 2 : 1 salts, 2–4. The central core, i.e. CH₂N(H)C(=O)C(=O)N(H)CH₂, of the isomeric di-cations are superimposable and chemically equivalent pairs of carbonyl, amide and pyridinium groups have an anti conformation. By contrast, the relative orientations of the terminal pyridinium rings from the central core vary significantly across the series as do the relative disposition of the acidic-H atoms. This feature of the structure influences the nature of N—H…O hydrogen bonding and, therefore, the observed supramolecular aggregation patterns. Thus, in 2, the syn-disposition of the nitrogen-bound hydrogen atoms enables the benzoate residue to interact via the two oxygen atoms with both pyridinium- and amine-H atoms to yield a zero-dimensional aggregate. By contrast, in each of 3 and 4, having further distance between the acidic-H atoms, the benzoate residues still interact (either through one both or both oxygen atoms) with pyridinium- and amine-H atoms but those derived from symmetry related molecules to generate one-dimensional aggregates. The three-dimensional architectures of 1–3 are consolidated, in the main, by C—H…O interactions. The structure of 1 revealed the benzoic acid residue to be perpendicular in contrast to the co-planar conforämations of the nitro groups. In the crystal packing, O–H…O hydrogen bonding lead to a helical supramolecular chain.