Hydrogen bonding versus π-interactions: their key competition in sildenafil solvates

Herein we report the X-ray characterization of four sildenafil solvates where the conformation of the pyrazolo[3,4-d]pyrimidine and phenyl rings depends on the solvent. It conditions the formation of an apparently innocent intramolecular H-bond that has a remarkable influence on the solid state architecture of the sildenafil solvates. DFT calculations indicate that a delicate balance between the energies of H-bonding and π-π (or lp-π) interactions are crucial.