4,6-Diamino­pyrimidine-2(1H)-thione hemihydrate: a three-dimensional hydrogen-bonded framework

In the title compound, C₄H₆N₄S·0.5H₂O, there are two independent pyrimidine­thione units, both of which lie across mirror planes in the space group Cmca. Hence, the H atoms bonded to the ring N atoms in each mol­ecule are disordered over two symmetry-related sites, each having an occupancy of 0.5. The water mol­ecule lies across a twofold rotation axis parallel to [010]. The mol­ecular components of (I) are linked by seven independent hydrogen bonds, of N-H...N, N-H...S, N-H...O and O-H...S types. A combination of disordered N-H...N hydrogen bonds and ordered N-H...S hydrogen bonds links the pyrimidine­thione units into a continuous tubular structure. The water mol­ecule acts as both a double donor of hydrogen bonds and a double acceptor, forming hydrogen bonds with components of four distinct pyrimidine­thione tubes, thus linking these tubes into a three-dimensional structure.