Photochemistry of the [Fe(CN)5NO]2––thiolate system
The studied system consists of [Fe(CN)5NO]2–1, mercaptosuccinate or another thiolate (RS–) and [Fe(CN)5N(O)SR]3–2 in equilibrium. The photochemical study has shown that both complexes 1 and 2 undergo either photooxidation or photoreduction, depending on the excited state energy. The present study is focused on the low energy effects, which consist of an inner-sphere photooxidation mode followed by a substitution pathway yielding pentacyanoferrate(III) complexes and NO or NOSR–˙ radicals for 1 and 2, respectively. In the presence of mercaptosuccinate the [FeIII(CN)5SR]3– complex 3 and nitrosomercaptosuccinate were identified as the most stable products. The photochemical reactivity of the [Fe(CN)5N(O)SR]3– complex thus resembles the photooxidation-substitution mode characteristic of [Fe(CN)5NO]2– but produces nitrosothiol instead of NO and needs considerably lower energy to be induced (MLCT band at λmax 526 nm). Consequently, the photoreactivity of 2 creates the possibility of using the 1–RS– system to photogenerate a nitrosothiol in situ using non-hazardous radiation.