Nonmerohedrally twinned 6-amino-3-methyluracil-5-carbaldehyde: a hydrogen-bonded ribbon containing four types of ring.

In the title compound [systematic name: 6-amino-5-formyl-3-methylpyrimidine-2,4(1H,3H)-dione], C(6)H(7)N(3)O(3), the intramolecular dimensions provide evidence for some polarization of the electronic structure. There is an intramolecular N-H...O hydrogen bond; this and a combination of three intermolecular N-H...O hydrogen bonds generate an almost planar ribbon containing S(6), R(2)(2)(4), R(2)(1)(6) and R(4)(4)(16) rings. These ribbons are linked into sheets by a dipolar carbonyl-carbonyl interaction. The structure was refined as a nonmerohedral twin, with twin fractions 0.7924 (1) and 0.2076 (10).