Photochemistry of the [Fe(CN)5NO]2––thiolate system

Abstract

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 [Fe^III(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 λ_max 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.