Racemic 5-(4-chlorophenyl)-2-methoxyindeno[1 ',2 ': 2,3]pyrido[5,6-d]pyrimidine-4,6(3H,5H)-dione-dimethylformamide (1/1) and (5RS,5aSR,10bSR)-10b-hydroxy-2-methoxy-5-(4-methoxyphenyl)-5a,10b-dihydroindeno[1 ',2 ': 2,3]pyrido[5,6-d]pyrimidine-4,6(3H,5H)-dione-dimethylformamide (1/1): chains of rings generated by N-H center dot center dot center dot O and C-H center dot center dot center dot pi(arene) hydrogen bonds

5-(4-Chlorophenyl)-2-methoxyindeno[1',2':2,3]pyrido[5,6-d]-pyrimidine-4,6(3H,5H)-dione crystallizes as a 1: 1 dimethylformamide solvate, C21H14ClN3O3.C3H7NO. The heterocyclic molecules contain a planar fused-ring system and they are linked by paired N-H...O hydrogen bonds [H...O = 1.85 Angstrom, N...O = 2.735 (4) Angstrom and N-H...O = 179degrees] into centrosymmetric dimers, which are themselves linked into chains by a single C-H...pi(arene) hydrogen bond. 10b-Hydroxy-2-methoxy-5-(4-methoxyphenyl)-5a,10b-dihydroindeno[10,20:2,3]pyrido[5,6-d] pyrimidine-4,6(3H,5H)-dione also crystallizes as a 1: 1 dimethylformamide solvate, C22H19N3O5.C3H7NO. The heterocyclic molecules contain a sharply folded fused-ring system and they are linked by two independent N-H...O hydrogen bonds [H...O = 1.92 and 2.18 Angstrom, N...O = 2.801 (2) and 3.051 (2) Angstrom, and N-H...O = 175 and 173degrees] into chains of rings. In both compounds, the dimethylformamide molecules are pendent from the chains, linked via N-H...O and O-H...O hydrogen bonds, respectively.