Two isomeric pairs of dihydrobenzo-pyrazoloquinazolines:: centrosymmetric dimers, chains and sheets built from C-H•••N and C-H•••π(arene) hydrogen bonds and π-π 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 center dot center dot center dot 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 center dot center dot center dot N and C - H center dot center dot center dot 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 center dot center dot center dot pi(arene) hydrogen bond, augmented by pi-pi stacking interactions.