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 Fe-2(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 (Phi(RSE) = 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 Fe-2(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, Fe-2(SR)(2)(NO)(3), undergoes second-order reaction with NO to regenerate the parent cluster with a rate constant of k(NO) = 1.1 x 10(9) M-1 s(-1) for R CH2CH2OH. Under aerated conditions the intermediate reacts with oxygen to give permanent photochemistry.