Photochemistry of the [Fe(CN)(5)N(O)SR](3-) complex - A mechanistic study

Photochemical behaviour of the title complex (RS- = mercaptosuccinate) was defined as photodissociation and photooxidation-substitution reactions indu ced by the MLCT transition. The stable products as well as shortly lived in termediate species were identified and characterised by ESR and fast UV/VIS spectroscopic methods. The photodissociation of excited [Fe(CN)(5)N(O)SR]( 3-) (Scheme 1, path a) shifts the equilibrium between the complex and [Fe(C N)(5)NO](2-) (Eq. (1)). Photooxidation-substitution reaction (Scheme 1, pat h b) leads to formation of the [Fe-III(CN)(5)SR](3-) complex and the RSNO.- radical. The radical generates different NO-donors in secondary thermal pr ocesses, which, however, have no noticeable influence on the nitrosation ca pacity of the system. Moreover, due to the fast reactions in equilibrium be tween nitroprusside and its thiolate derivative (Eq. (1)), the photooxidati on-substitution is really a photocatalytic process and the nitrosation agen ts are produced mostly at the expense of nitroprusside, whereas the [Fe(CN) (5)N(O)SR](3-) complex behaves as a photocatalyst. Its photoreactivity indu ced by visible light (lambda (max) = 526 nm, epsilon (max) = 6000) reduces the threshold energy of the process to nearly the phototherapeutic window. (C) 2001 Elsevier Science B.V. All rights reserved.