The interaction of Ca2+-ions with sildenafil citrate (Viagra) leads to the precipitation of a new polymorph variety of sildenafil base. Under the same conditions, Mg2+, Zn2+, and Cd2+ ions form structurally related crystalline complexes of the composition Me2+C28H34N6O11S. Lattice parameters have been determined showing that magnesium compound belongs to an orthorhombic system, while the zinc and cadmium compounds are its monoclinic distortions. All three compounds are thermally stable, undergoing decomposition above 175 degrees C with the consequent formation of carbonates Me2+CO3 and oxides. (c) 2005 Wiley-Liss, Inc.