Photochemical Investigation of Roussin's Red Salt Esters:  Fe2(μ-SR)2(NO)4

The photochemistry of various Roussin's red ester compounds of the general formula Fe2(SR)2(NO)4, where R = CH3, CH2CH3, CH2C6H5, CH2CH2OH, and CH2CH2SO3 -, were investigated. Continuous photolyses of these ester compounds in aerated solutions led to the release of NO with moderate quantum yields for the photodecomposition of the ester (ΦRSE = 0.02−0.13). Electrochemical studies using an NO electrode demonstrated that 4 mol of NO are generated for each mole of ester undergoing photodecomposition. Nanosecond flash photolysis studies of Fe2(SR)2(NO)4 (where R = CH2CH2OH and CH2CH2SO3 -) indicate that the initial photoreaction is the reversible dissociation of NO. In the absence of oxygen, the presumed intermediate, Fe2(SR)2(NO)3, undergoes second-order reaction with NO to regenerate the parent cluster with a rate constant of k NO = 1.1 × 109 M-1 s-1 for R = CH2CH2OH. Under aerated conditions the intermediate reacts with oxygen to give permanent photochemistry.