Synthesis, crystal structure at 219 K and Hirshfeld surface analyses of 1,4,6-tri­methyl­quinoxaline-2,3(1H,4H)-dione monohydrate

The asymmetric unit of the title compound, C11H12N2O2H2O, contains a molecule of 1,4,6-trimethyl-1,4-dihydroquinoxaline-2,3-dione and a solvent water molecule. Four atoms of the benzene ring are disordered over two sets of sites in a 0.706 (7):0.294 (7) ratio while the N-bound methyl groups are rotationally disordered with occupancy ratios of 0.78 (4):0.22 (4) and -0.76 (5):0.24 (5). In the crystal, molecules are linked by O—HO and C—HO hydrogen bonds into layers lying parallel to (101). The Hirshfeld surface analysis indicates that the most important contributions to the packing arrangement are due to HH (51.3%) and OH/HO (28.6%) interactions. The molecular structure calculated by density functional theory is compared with the experimentally determined molecular structure, and the HOMO–LUMO energy gap has been calculated.