Stabilization and electron spin resonance characterization of Ru(bpy)3(3+) in silica gel by chemical oxidation and photoinduced electron transfer

The stabilization of Ru(bpy)(3)(3+) from Ru(bpy)(3)(2+) at both 77 K and room temperature in silica gel by chemical oxidation with chlorine gas and by photoinduced electron transfer to suitable electron accepters is reported. Stabilization at room temperature is of paticular interest for potential light energy storage systems. Paramagnetic Ru(bpy)(3)(3+) is characterized by electron spin resonance spectroscopy. The Ru(bpy)(3)(3+) yield formed by chlorine gas oxidation can be controlled by the silica gel pore size and decreases with increasing pore size. The Ru(bpy)(3)(3+) yield is 1 order of magnitude smaller in 14.0 nm pore silica gel compared to 2.5 nm pore silica gel. The Ru(bpy)(3)(3+) yield gradually decreases by preheating the silica gel to higher temperatures before impregnation with Ru(bpy)(3)(2+) These results suggest that the oxidation of Ru(bpy)(3)(2+) with chlorine gas takes place via a silica gel surface mediated reaction and that the direct reaction of adsorbed Ru(bpy)(3)(2+) with a chlorine molecule in the gas phase is less effective. Ru(bpy)(3)(3+) can also be stabilized in silica gel by photolysis in the presence of the electron acceptor S2O82- (persulfonate ion) with a 50% yield or tetrachloro-1,4-benzoquinone (p-chloranil) with a lower yield.