Isomeric pyrazolo[3,4-d]pyrimidine-based molecules: disappearance of dimerization due to interchanged substitutions.

In 5-benzyl-1,7-dimethyl-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-d]pyrimidine-4,6-dione, C(14)H(14)N(4)O(2), which crystallizes in space group P 1 macro, weak intermolecular C[bond]H...O hydrogen bonds generate dimers. The isomeric compound 1-benzyl-5,7-dimethyl-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-d]pyrimidine-4,6-dione, C(14)H(14)N(4)O(2), crystallizes in space group P2(1)/n, and shows no such dimerization. Instead, it exhibits C[bond]H...pi interactions with the phenyl ring. In both structures, the molecules are linked by aromatic pi-pi-stacking interactions.