Synthesis, crystal structure at 219†K and Hirshfeld surface analyses of 1,4,6-tri-methyl-quinoxaline-2,3(1H,4H)-dione monohydrate.

The asymmetric unit of the title compound, C(11)H(12)N(2)O(2)·H(2)O, contains a mol-ecule of 1,4,6-trimethyl-1,4-di-hydro-quinoxaline-2,3-dione and a solvent water mol-ecule. 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, mol-ecules are linked by O-H⋯O and C-H⋯O hydrogen bonds into layers lying parallel to (10). The Hirshfeld surface analysis indicates that the most important contributions to the packing arrangement are due to H⋯H (51.3%) and O⋯H/H⋯O (28.6%) inter-actions. The mol-ecular structure calculated by density functional theory is compared with the experimentally determined mol-ecular structure, and the HOMO-LUMO energy gap has been calculated.