A hydrogen-bonded ribbon in 6-amino-3-methyl-5-nitroso-2-(pyrrolidin-1-yl)pyrimidin-4(3H)-one monohydrate and hydrogen-bonded sheets in 6-amino-2-dimethylamino-3-methyl-5-nitrosopyrimidin-4(3H)-one monohydrate.

In each of 6-amino-3-methyl-5-nitroso-2-(pyrrolidin-1-yl)pyrimidin-4(3H)-one monohydrate, C(9)H(13)N(5)O(2).H(2)O, (I), and 6-amino-2-dimethylamino-3-methyl-5-nitrosopyrimidin-4(3H)-one monohydrate, C(7)H(11)N(5)O(2).H(2)O, (II), the interatomic distances indicate significant polarization of the electronic structures of the pyrimidinone molecules. In each compound, the organic component contains an intramolecular N-H...O hydrogen bond. The molecular components in (I) are linked by a combination of two-centre O-H...O, O-H...N and N-H...O hydrogen bonds and a three-centre O-H...(NO) hydrogen bond to form a broad ribbon containing five distinct ring motifs. In compound (II), three intermolecular hydrogen bonds, one each of the O-H...O, O-H...N and N-H...O types, link the molecules into sheets containing equal numbers of centrosymmetric R(4)(4)(10) and R(10)(8)(34) rings.