Effect of water and light on the stability of transition metal nitroprussides

Transition metal nitroprussides form an interesting family of coordination polymers with a 3D porous framework and appropriate properties for energy conversion and storage, photocatalysis, electrochemical devices, gas separation and storage, among other many potential applications. The stability of sodium nitroprusside in aqueous solution in the presence of light has been intensively studied related to its medical applications as a potent hypotensive agent. The stability of the corresponding transition metal salts in environmental conditions, where water molecules and light are always present, remains undocumented, and it is relevant for such potential applications as functional materials. In this contribution, we are reporting the results of a study on the effect of water and light on the stability of these solids in aqueous suspension under illumination and in the darkness, and in environmental conditions. The degradation process in water suspension was monitored from pH measurements and the recovered solid fractions were characterized by IR and and Mössbauer spectroscopies. The observed behavior evidences that the metal linked at the N end of CN ligands in the nitroprusside building block plays a relevant role in the extent of photodegradation. A metal with a high ability to subtract electron density from the nitroprusside ion generates a higher photostability for this last one.