Two isomeric pairs of dihydrobenzopyrazoloquinazolines: centrosymmetric dimers, chains and sheets built from C-H...N and C-H...pi(arene) hydrogen bonds and pi-pi stacking interactions.

Molecules of 5-methyl-2-phenyl-6,7-dihydrobenzo[h]pyrazolo[1,5-a]quinazoline, C21H17N3, (I), are linked into chains by a combination of a C-H...pi(arene) hydrogen bond and a pi-pi stacking interaction; in the closely related 5-methyl-2-(4-methylphenyl)-6,7-dihydrobenzo[h]pyrazolo[1,5-a]quinazoline, C22H19N3, (II), there are no hydrogen bonds and the molecules are linked into centrosymmetric dimers by a pi-pi stacking interaction. 7-Methyl-10-phenyl-5,6-dihydrobenzo[h]pyrazolo[5,1-b]quinazoline, C21H17N3, (III), is isomeric with (I), and the molecules of (III) are linked into sheets by a combination of C-H...N and C-H...pi(arene) hydrogen bonds. 7-Methyl-10-(4-methylphenyl)-5,6-dihydrobenzo[h]pyrazolo[5,1-b]quinazoline, C22H19N3, (IV), is isomeric with (II), and molecules of (IV) are linked into centrosymmetric dimers by a C-H...pi(arene) hydrogen bond, augmented by pi-pi stacking interactions.