Cyclic heterotetrameric and low-dimensional hydrogen-bonded polymeric structures in the morpholinium salts of ring-substituted benzoic acid analogues

The morpholinium (tetrahydro-2H-1,4-oxazin-4-ium) cation has been used as a counter-ion in both inorganic and organic salt formation and particularly in metal complex stabilization. To examine the influence of interactive substituent groups in the aromatic rings of benzoic acids upon secondary structure generation, the anhydrous salts of morpholine with salicylic acid, C4H10NO+·C7H5O3−, (I), 3,5-dinitrosalicylic acid, C4H10NO+·C7H3N2O7−, (II), 3,5-dinitrobenzoic acid, C4H10NO+·C7H3N2O6−, (III), and 4-nitroanthranilic acid, C4H10NO+·C7H5N2O4−, (IV), have been prepared and their hydrogen-bonded crystal structures are described. In the crystal structures of (I), (III) and (IV), the cations and anions are linked by moderately strong N—H...Ocarboxylhydrogen bonds, but the secondary structure propagation differs among the three,viz.one-dimensional chains extending along [010] in (I), a discrete cyclic heterotetramer in (III), and in (IV), a heterotetramer with amine N—H...O hydrogen-bond extensions alongb, giving a two-layered ribbon structure. With the heterotetramers in both (III) and (IV), the ion pairs are linked though inversion-related N—H...Ocarboxylatehydrogen bonds, giving cyclicR44(12) motifs. With (II), in which the anion is a phenolate rather than a carboxylate, the stronger assocation is through a symmetric lateral three-centre cyclicR12(6) N—H...(O,O′) hydrogen-bonding linkage involving the phenolate and nitro O-atom acceptors of the anion, with extension through a weaker O—H...Ocarboxylhydrogen bond. This results in a one-dimensional chain structure extending along [100]. In the structures of two of the salts [i.e.(II) and (IV)], there are also π–π ring interactions, with ring-centroid separations of 3.5516 (9) and 3.7700 (9) Å in (II), and 3.7340 (9) Å in (IV).