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

Abstract

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...Ocarboxyl hydrogen 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 along b, giving a two-layered ribbon structure. With the heterotetramers in both (III) and (IV), the ion pairs are linked though inversion-related N-H...Ocarboxylate hydrogen bonds, giving cyclic R4(4)(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 cyclic R1(2)(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...Ocarboxyl hydrogen 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).

Supramolecular association in the triclinic (Z′=1) and monoclinic (Z′=4) polymorphs of 4-(4-acetylphenyl)piperazin-1-ium 2-amino-4-nitrobenzoate

“…Thus, the sodium dihydrate [3], potassium hydrate [3], rubidium hydrate [4] and caesium dihydrate [5] with higher coordination numbers for the larger alkali cations being achieved through bridging water molecules and the increased participation of nitro-O atoms in coordination. The remaining structures, namely of ammonium salts, often feature extensive hydrogen bonding interactions: ammonium hydrate [6], dimethyl-and di-nbutyl-ammonium [7], di-cyclohexylammonium [8], hydrazinium [9], morpholin-4-ium [10], guanidinium hydrate [11] as well as an example of a diammonium salt, namely ethylenediammonium, characterised as a dihydrate [12]. The only example of a metal complex with the anion is that of a binary lead(II) species [13].…”