Photochemical behaviour of ion pairs of the type {[Cr(en)3]3+; [M(CN)6]4−} (MFe, Ru, Os) as a first example of second-sphere photoeffects of chromium(III) amine complexes

✍ Scribed by R. Billing; H. Hennig

• Book ID: 103993830
• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 658 KB
• Volume: 63
• Category: Article
• ISSN: 1010-6030
• DOI: 10.1016/1010-6030(92)85148-n

✦ Synopsis

Ion pairs of the constitution ([Cr(en),]'*; [M(CN)$-) show, in an aqueous buffer solution, second-sphere charge transfer (SSCT) absorption bands at 342 nm (M=Fe), 290 nm (MS Ru) and 303 nm (M=Os) additionally to the spectra of the individual components. Two possible mechanisms of the optical electron transfer process involving the initial formation of low spin (tzg4) and high spin (t2: e&l) [Cr(en),]*+ respectively are discussed in order to explain the rather high energies of the SSCT absorption maxima. The ion pairs under discussion undergo photosubstitution reactions upon ligand field excitation (Ai,,= 450 nm) of the chromium complex. Binuclear complexes [(H,O)(en),Cr-NC-M(CN),]-(M=Fe, Ru, OS) are formed, which are distinguished by intense metal-to-metal charge transfer absorption bands in the UV spectral region. These binuclear complexes do not undergo further photoreactions. Photoredox reactions, indicated by the formation of [M(CN),13-(M = Ru, OS), are initiated upon excitation of the SSCT transition (Aim=320 nm) within the ion pair compounds. Additionally, also photosubstitution is observed upon short-wavelength irradiation.