Mixed-ligand complexes photooxidation

Most of the reported photochemical reactions of lanthanide complexes involve some type of redox behavior.147 Photolysis (254—405 nm) of Eu2+ in acidic aqueous solution, for example, results in photooxidation of the metal and generation of H2 (equation 50).148 While the excited states responsible for this reaction nominally arise from 4/ -+ 5d transitions localized on the metal, strong mixing of the 5rf-orbital with ligand orbitals endows these states with appreciable CTTL character. Photoreduction of aquated Eu3+ can also be driven with UV ( 254 nm) light149 and forms the... 

Arakawa and coworkers [45] developed the on-line photoreaction cell depicted in Figure 5.3 and performed a series of studies on the detection of reaction intermediates in photosubstitution and photooxidation of Ru(II) complexes. The photosubstitution of Ru(bpy)2B [bpy = 2,2 -bipyridine B = 3,3 -dimethyl-2,2 -bipyridine (dmbpy) or 2-(aminomethyl)pyridine (ampy)] was studied in acetonitrile and pyridine. Irradiation of Ru(bpy)2B and related complexes yields a charge-transfer excited species with an oxidized Ru center and an electron localization on the bpy moiety. The excited-state complex underwent ligand substitution via a stepwise mechanism that includes ant] bidentate ligand (Scheme 5.6). Photoproducts such as Ru(bpy)2S2 (S = solvent molecule) and intermediates with a monodentate (mono-hapfo-coordination) B ligand, Ru(bpy)2BS, and Ru(bpy)2BSX+ (X=C10/, PF ) were detected. Other studies also identified photo-oxidized products of several mixed-valence Ru(II) complexes upon irradiation (7i> 420 nm) [31b, 46]. 

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