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

In the title compound, C(4)H(6)N(4)S·0.5H(2)O, 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.