10-(4-chlorophenyl)-7-methyl-5,6-dihydrobenzo[h]pyrazolo[5,1-b]quin-azoline and 2-(4-chlorophenyl)-5-methyl-6,7-dihydrobenzo[h]pyrazolo-[1,5-a]quinazoline: isomeric molecules linked into hydrogen-bonded dimers or pi-stacked chains

The isomeric title compounds 10-(4-chlorophenyl)-7-methyl-5,6-dihydrobenzo[h]pyrazolo[5,1-b]quinazoline, (I), and 2-(4-chlorophenyl)-5-methyl-6,7-dihydrobenzo[h]pyrazolo[1,5-a]-quinazoline, (II), both C21H16ClN3, exhibit peripheral delocalization in the heteroaromatic portion of the fused ring system. The molecules of ( I) are linked into centrosymmetric dimers by a single C-H...pi( arene) hydrogen bond, and the molecules of (II), where Z' = 2, are linked by pi-pi stacking interactions into chains in which the two types of molecules alternate.