Crystal structures of the 1:1 salts of 2-amino-4-nitrobenzoate with each of (2-hydroxyethyl)dimethylazanium, tert-butyl(2-hydroxyethyl)azanium and 1,3-dihydroxy-2-(hydroxymethyl)propan-2-aminium

Three ammonium salts of 2-amino-4-nitrobenzoate are described. Based on N—H⋯O and O—H⋯O hydrogen-bonding involving the different constituents, supramolecular chains, tubes and double-layers are found in their crystals.


Structural commentary
The molecular structures of the constituent ions in (I) are shown in Fig. 1 and selected geometric data for this and for (II) and (III), are collected in Table 1. That proton transfer occurred during co-crystallization is confirmed by the experimental equivalence of the C7 . . . O1, O2 bond lengths of 1.270 (2) and 1.258 (2) Å , respectively, in the 2-amino-4nitrobenzoate anion and in the pattern of hydrogen-bonding interactions, as described below in Supramolecular features. In the anion, the carboxylate group is tilted out of the plane of the benzene ring to which it is connected with the dihedral angle being 6.7 (3) . Similarly, the nitro group lies out of the plane of the benzene ring, forming a dihedral angle of 6.6 (3) . A dis-rotatory relationship between the carboxylate and nitro substituents is indicated by the dihedral angle between them of 11.5 (4) . An intramolecular amine-N1-HÁ Á Á O1(carboxylate) hydrogen-bond is noted which closes an S(6) loop, Table 2. In the Me 2 N (+) (H)CH 2 CH 2 OH cation, the N3-C8-C9-O5 torsion angle of À71.15 (19) is indicative of a Àsyn-clinal conformation.
The anion in (II), Fig. 2, presents essentially the same features as just described for (I), Tables 1 and 3, with the exception of the con-rotatory relationship between the carboxylate and nitro substituents. The (t-Bu)N (+) H 2 (CH 2-CH 2 OH) cation is relatively rare, being reported for the first time in its salt with sulfathiazolate only in 2012 (Arman et al.,   The molecular structures of the ions comprising the asymmetric unit of (II) showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level. The dashed line indicates a hydrogen bond.

Figure 3
The molecular structures of the ions comprising the asymmetric unit of (III) showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level.

Figure 1
The molecular structures of the ions comprising the asymmetric unit of (I) showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level. Dashed lines indicate a hydrogen bonds. 2012). As for the cation in (I), the N3-C12-C13-O5 torsion angle for the cation in (II) of À55.18 (18) is indicative of a Àsyn-clinal conformation.

Supramolecular features
As expected from the chemical compositions of (I)-(III), significant charge-assisted hydrogen-bonding is apparent in their respective crystals. Geometric data characterizing these and other identified interactions are collated in Tables 2-4, respectively.
In the crystal of (III), supramolecular double-layers in the bc-plane are formed as a result of charge-assisted ammonium-N3-HÁ Á ÁO(carboxylate), ammonium-N3-HÁ Á ÁO(hydroxy) and hydroxy-O-HÁ Á ÁO(carboxylate) hydrogen-bonds. The ammonium-N3-H3N atom is bifurcated, forming two weak ammonium-N3-HÁ Á ÁO(hydroxy) hydrogen-bonds. A view normal to the plane of the double-layer and a side-on view are shown in Fig. 6(a) and (b), respectively. From the latter, the intra-layer region comprises the ammonium groups, each of which forms four N-HÁ Á ÁO hydrogen-bonds to carboxylate and hydroxy groups on either side. Each hydroxy group of the cation forms a hydroxy-O-HÁ Á ÁO(carboxylate) hydrogenbond with a carboxylate-O atom derived from a different anion, and each accepts an ammonium-N-H atom derived from a different cation. Each carboxylate-O atom forms two hydrogen-bonds, the O1 accepts hydrogen-bonds from different hydroxy groups, and the O2 atom accept hydrogenbonds from hydroxy and ammonium groups. Projecting to either side of the double-layer are the nitrobenzene groups, Fig. 6(c) and (d). These provide the links to construct the three-dimensional architecture, i.e. via amine-N-HÁ Á Á O(nitro) interactions, involving both nitro-O atoms.
The obvious trend from the present study is the increase in dimensionality of the supramolecular aggregation pattern, i.e. chain in (I), tube in (II) and double-layer in (III), as the number of acidic ammonium-N-H atoms increases.

Database survey
As indicated in the Chemical context, a number of ammonium salts of the anion derived from 2-amino-4-nitrobenzoic acid have now been described. The key conformational indicators for the anion are the dihedral angles formed between CO 2 /C 6 / NO 2 . The smallest dihedral angles between the CO 2 /C 6 , C 6 / NO 2 and CO 2 /NO 2 pairs of least-squares planes of 3.44 (14), 0.69 (11) and 3.2 (2) are found for the anion in the salt with H 3 N (+) CH 2 CH 2 N (+) H 3 (Smith et al., 2002). Conversely, the greatest CO 2 /C 6 , C 6 /NO 2 and CO 2 /NO 2 dihedral angles of   (14) , respectively, are found in the N (+) H 4 (Smith, 2014b), n-Bu 2 N (+) H 2  and H 2 NN (+) H 3 (Wardell et al., 2017) salts, respectively. The respective dihedral angles in (I)-(III), described herein, fall within these ranges.

2-Amino-4-nitrobenzoate tert-butyl(2-hydroxyethyl)azanium (II)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.24 e Å −3 Δρ min = −0.33 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.