Sildenafil citrate (Viagra) complexes with bivalent ions.

The interaction of Ca(2+)-ions with sildenafil citrate (Viagra) leads to the precipitation of a new polymorph variety of sildenafil base. Under the same conditions, Mg(2+), Zn(2+), and Cd(2+) ions form structurally related crystalline complexes of the composition Me(2+)C(28)H(34)N(6)O(11)S. 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 Me(2+)CO(3) and oxides.