Crystal structure of 2-ethyl-4-methyl-1-(2-oxido-3,4-dioxo­cyclo­but-1-en-1-yl)-1H-imidazol-3-ium

In the title inner salt molecule, C10H10N2O3, the four-membered cyclobutene ring is twisted by 7.1 (2)° with respect to the five-membered imidazole ring. The crystal packing exhibits an R22(9) hydrogen-bonding ring motif through N—H⋯O and C—H⋯O inter­actions. The potential non-linear optical properties were studied by a computational ab initio calculations performed at the DFT/B3LYP/6–31++G(d,p) level of theory.