Hybrid azine–oxamic acid molecular design: synthesis, structure, and supramolecular implications

Abstract

Since the 1960s, oxamic acid derivatives and their coordination compounds have been extensively studied, with applications ranging from protective agents for marble to biologically relevant systems. However, no reports exist on hybrid molecules combining an azine group with an oxamic acid-derived group. The azine group is notable for its photochromic properties and π-conjugation, which make it valuable in fields such as biomedicine, optoelectronics, and chemical sensing. This work reports the synthesis and structural characterization of two novel molecules incorporating both azine and oxamic acid-derived groups: the ester form, named NN-Et₂H₂oba, and the acid form, NN-H₄oba. The synthesis was initiated by forming the azine group from 2-nitrobenzaldehyde and hydrazine dichlorohydrate, followed by a reduction of the nitro groups and subsequent addition of the oxamic acid-derived group. Based on the structures obtained by single-crystal X-ray diffraction (SXRD), correlations were established with data from FTIR, ¹H NMR, and elemental analysis. Additionally, given the critical role of intermolecular interactions in determining material properties, a comprehensive study of nature and energies of the non-covalent interactions was conducted using computational methods, including Hirshfeld surface analysis, fingerprint plots, energy framework diagrams, and crystal lattice energy calculations. Intramolecular N–H⋯N hydrogen bonds, present in both molecules, as well as intermolecular C–H⋯O interactions observed in NN-Et₂H₂oba, were found to significantly contribute to the stabilization of molecular planarity. This structural conformation endows the molecules with potential for photophysical applications. Moreover, the supramolecular organization of NN-Et₂H₂oba is primarily stabilized by London dispersive forces, while that of NN-H₄oba is stabilized by both dispersive forces and hydrogen bonds.