Direct evidence for chemically distinct regions within nation films on electrodes

Abstract Electrochemical and spectroelectrochemical experiments on the complexes [(bpy) 2 (py)Ru II (OH 2 )] 2+ and [(trpy)(bpy)Ru II (OH 2 )] 2+ (py is pyridine; bpy is 2,2'-bipyridine; trpy is 2,2',2“-terpyridine) with Nation films coated on electrodes demonstrate that the complexes partition amongst three chemically distinct regions or phases. As Ru(II) the complexes reside both in an electroinactive phase and, based on the pH dependence of the Ru(III)/(II) couples, e.g., [(bpy) 2 (py)Ru III (OH)] 2+ /[(bpy) 2 (py)Ru II (OH 2 )] 2+ , in two electroactive phases. Partitioning amongst the three phases depends on the pH of the external solution and on the oxidation state and proton content of the complex. Addition of alcohols releases the complex from the electroinactive phase but at the expense of loss of the bound water molecule and binding to the sulfonate sites by anation and, therefore, to a fourth distinct chemical or physical state in which the complex can exist within Nation films.