10-Methylisoalloxazine 5-oxide from synchrotron powder diffraction data

The title compound [systematic name: 10-methylbenzo[g]pteridine-2,4(3H,10H)-dione 5-oxide], C11H8N4O3, consists of a large rigid isoalloxazine group which is approximately planar (r.m.s. deviation = 0.037 Å). In the crystal, intermolecular N—H...O hydrogen bonds link the molecules into centrosymmetric dimers. Dimers related by translation along the c axis form stacks through π–π interactions [centroid–centroid distances = 3.560 (5) and 3.542 (5) Å]. Weak intermolecular C—H...O interactions further consolidate the crystal packing.