Structural characterization of a new dioxamic acid derivative by experimental (FT-IR, NMR, and X-ray) analyses and theoretical (HF and DFT) investigations

Very few investigations concerning the crystal structure and chemical properties of dioxamic acids have been related in the literature. This work describes the chemical properties of ortho-phenylenebis(oxamic acid) (2) and its new derivative, hydrogeno ortho-phenylenebis(oxamato) benzimidazolium (3) using experimental (FT-IR, NMR, and X-ray single crystal diffraction) and theoretical (HF/3-21G* and B3LYP/6-31G* calculations) methodologies. Compound 2 displays intramolecular hydrogen bonding between the hydrogen of an amide group and the oxygen atom of another amide group present in the structure. Compound 3 was prepared by a newly developed synthetic route involving decomposition of the dioxamic acid in solution without the presence of metallic ions. Thermodynamic calculations indicate a process via two successive hydrolyzes of the amide groups of 2, followed by condensation with formic acid and finally dehydration. The structure of 3 was solved by X-ray single-crystal diffraction and it consists of meso-helical chains stabilized by intra and intermolecular hydrogen bonds and π–π stacking interactions.

► Synthesis of ortho-phenylene(oxamic) acid.
► A new synthetic route involving decomposition of the dioxamic acid.
► Structural characterization of the hydrogeno ortho-phenylenebis(oxamato) benzimidazolium.
► Helical structure stabilized by intra and intermolecular hydrogen bonds and π–π stacking interactions.