Four 2-aryl-8,8-dimethyl-6,7,8,9-tetrahydropyrazolo[2,3-a]quinazolin-6-ones: isolated molecules, hydrogen-bonded dimers, and pi-stacked chains of hydrogen-bonded dimers

In each of the three compounds 2-(4-chlorophenyl)-5,8,8-trimethyl-6,7,8,9- tetrahydropyrazolo[ 2,3-a] quinazolin-6-one, C19H18ClN3O, ( I), 2-(4-methoxyphenyl)-5,8,8-trimethyl-6,7,8,9-tetrahydropyrazolo[ 2,3-a] quinazolin-6-one, C20H21N3O2, (II), and 8,8-dimethyl-2-(4-methylphenyl)-6,7,8,9-tetrahydropyrazolo[ 2,3- a] quinazolin-6-one monohydrate, C19H19N3O center dot H2O, (IV), the non-aromatic carbocyclic ring adopts a half-chair conformation, while in 2-(4-chlorophenyl)-8,8-dimethyl-5-phenyl- 6,7,8,9-tetrahydropyrazolo[2,3-a] quinazolin-6-one, C24H20ClN3O, (III), the corresponding ring adopts a conformation intermediate between the envelope and screw - boat forms. The structure of ( I) consists of isolated molecules, while that of ( II) contains dimers formed by C - H center dot center dot center dot O hydrogen bonds. In ( III), dimers formed by C - H center dot center dot center dot O hydrogen bonds are linked into chains by means of an aromatic pi-pi stacking interaction, while in the monohydrate, ( IV), the heterocyclic molecules and the water molecules are linked by O - H center dot center dot center dot O and O - H center dot center dot center dot N hydrogen bonds to form centrosymmetric four-component aggregates.