Four products from the cyanoacetylation of pyrimidines: hydrogen-bonded dimers, pi-stacked hydrogen-bonded chains and hydrogen-bonded chains of edge-fused rings.

The molecules of 2-[6-amino-3-methyl-2-(methylsulfanyl)-4-oxo-3,4-dihydropyrimidin-5-ylcarbonyl]acetonitrile, C(9)H(10)N(4)O(2)S, (I), are linked in pairs by N-H...O hydrogen bonds to form cyclic centrosymmetric R(2)(2)(4) dimers. Similar dimers formed by 2-(6-amino-1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-5-ylcarbonyl)acetonitrile, C(9)H(10)N(4)O(3), (II), are reinforced by paired N-H...N hydrogen bonds and linked into chains of rings by C-H...O hydrogen bonds. The molecules of 2-cyano-N-[6-methoxy-2-(methylsulfanyl)pyrimidin-4-yl]acetamide, C(9)H(10)N(4)O(2)S, (III), are linked into simple C(6) chains by an N-H...N hydrogen bond, and the chains are weakly linked into sheets by a pi-pi stacking interaction. A combination of one two-centre N-H...N hydrogen bond and one three-centre C-H...(N,O) hydrogen bond links the molecules of 2-cyano-N-[6-chloro-2-(methylsulfanyl)pyrimidin-4-yl]acetamide, C(8)H(7)ClN(4)OS, (IV), into a chain of alternating edge-fused R(2)(1)(6) and R(1)(2)(6) rings. The crystal structures reported in this study, and those of some related examples from the recent literature, show a wide variation in hydrogen-bonded aggregation consequent upon rather small changes in molecular constitution.