Four 7-aryl-substituted pyrido[2,3-d]pyrimidine-2,4(1H,3H)-diones: similar molecular structures but different crystal structures.

Molecules of 1,3-dimethyl-7-(4-methylphenyl)pyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione, C(16)H(15)N(3)O(2), (I), are linked by paired C-H...O hydrogen bonds to form centrosymmetric R(2)(2)(10) dimers, which are linked into chains by a single pi-pi stacking interaction. A single C-H...O hydrogen bond links the molecules of 7-(biphenyl-4-yl)-1,3-dimethylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione, C(21)H(17)N(3)O(2), (II), into C(10) chains, which are weakly linked into sheets by a pi-pi stacking interaction. In 7-(4-fluorophenyl)-3-methylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione, C(14)H(10)FN(3)O(2), (III), an N-H...O hydrogen bond links the molecules into C(6) chains, which are linked into sheets by a pi-pi stacking interaction. The molecules of 7-(4-methoxyphenyl)-3-methylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione, C(15)H(13)N(3)O(3), (IV), are also linked into C(6) chains by an N-H...O hydrogen bond, but here the chains are linked into sheets by a combination of two independent C-H...pi(arene) hydrogen bonds.