2-Aminobenzoxazole–oxalic acid (2/1)

In the title compound, proton transfer from oxalic acid to the N atom of the heterocycle has occurred to form a 2:1 molecular salt. In the extended structure, N—H⋯O hydrogen bonds link the components into [100] chains, which feature R 2 2(8) and R 4 4(14) loops.

In the title compound, 2C 7 H 7 N 2 O + •C 2 O 4 2À , proton transfer from oxalic acid to the N atom of the heterocycle has occurred to form a 2:1 molecular salt.In the extended structure, N-H� � �O hydrogen bonds link the components into [100] chains, which feature R 2 2 (8) and R 4 4 ( 14) loops.

Structure description
2-Aminobenzoxazole has gained significant attention in the field of organic chemistry due to its diverse range of applications and properties.This heterocyclic compound exhibits intriguing structural features and has demonstrated potential utility in the development of pharmaceuticals and agrochemicals and in materials science (Hwang et al., 2006;Potashman et al., 2007).With its aromatic and nitrogen-containing structural motifs, 2-aminobenzoxazole has emerged as a key scaffold for the synthesis of biologically active molecules and advanced materials.Herein, we report on the crystal structure analysis of a new 2-aminobenzoxazole-oxalic acid molecular salt.
The identification of the co-crystal as a salt is based on the successful refinement of the relevant H atoms using X-ray data.The proton transfer is further supported by the C-O distances [O4-C15 = 1.266 (2) A ˚, O3-C15 = 1.234 (2) A ˚, O5-C16 = 1.272 (2) A ˚and O6-C16 = 1.222 (2) A ˚] with differences between the bond lengths within each group of 0.032 and 0.050 A ˚; these differences differ from those for O-C distances in deprotonated carboxyl groups.In nondeprotonated oxalic acid, these differences are greater (Sasaki et al., 2020).The mean planes of the carboxylic fragments in the OXL ion are turned by 10.13 (4) � from each other.In the crystal, the 2BAO and OXL ions are not coplanar, the 2ABO ions being inclined to the OXL ions by 18.81 (3) and 16.00 (5) � .The dihedral angle between the 2ABO ions is 37.52 (2) � .

Figure 2
The crystal structure of the organic salt structure of 2ABO and OXL viewed along the c axis.

Figure 1
The organic salt structure of 2ABO and OXL.Displacement ellipsoids are drawn at the 50% probability level and N-H� � �O hydrogen bonds are shown as dashed lines.
for evaporation.After about 3 weeks, cube-like single crystals of the title salt suitable for data collection were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

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.

data reports data-2
IUCrData (2024).9, x240033 Refinement.The hydrogen atoms of amino groups and protonated nitrogen atoms of oxzole groups were located in difference -Fourier maps and refined with restrained distances of 0.85±(1) Å.The H atoms of the benzene ring were calculated geometrically with C-H = 0.93 Å and U iso (H) = 1.2U eq (C).

Figure 3 A
Figure 3 A fragment of a [100] chain in the extended structure of the title compound with hydrogen bonds shown as dashed lines.

Table 2
Experimental details.