A serendipitous synthesis of N,N′-Diethyloxamide: crystallographic and computational analysis of its solid-state structure

Abstract A combined crystallographic/computational analysis focused on the supramolecular features of the crystal structure of N,N′-diethyloxamide (NNDO) is discussed in this work. The studied compound was obtained unexpectedly during the synthesis of a series of salts of cyclic oximes derivatives. In the solid state NNDO is stabilized essentially through a strong N–H···O hydrogen bond but Hirshfeld surface analysis and Density Functional Theory (DFT) calculations were carried out to evaluate the strength of the predominant hydrogen bonds observed in the X-ray structure, as well as the secondary C–H···O and C–H···N contacts established between the ethyl groups and the perpendicular dioxamide group. These interactions were further investigated using a combination of Quantum Theory of Atoms in Molecules (QTAIM), Non-Covalent Interaction Plot (NCIplot) and natural bond orbital (NBO) analysis computational tools, and were rationalized using Molecular Electrostatic Potential (MEP) surface, electron localization function (ELF), localized orbital locator (LOL) and Fukui function calculations. The insights gathered in this study enrich the understanding of the factors governing crystal packing in amides and related compounds.