Ion-pair complexes of methyl viologen and anionic solutes

✍ Scribed by J.P. Kuczynski; B.H. Milosavljevic; A.G. Lappin; J.K. Thomas

• Publisher: Elsevier Science
• Year: 1984
• Tongue: English
• Weight: 276 KB
• Volume: 104
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(84)80185-2

✦ Synopsis

Methyl viologen forms ion-pair complexes with anionic solutes such as EDTA, hexametaphosphate, acetate, citrate and sulfide ions. The luminescence properties of all complexes are similar, exhibiting an emission maximum centered about 520 nm and an excitation peak at 405 nm. The lifetime of the luminescence is on the order of 5 ns. For all complexes a new absorption band appears as a shoulder extending out to 500 nm. For the EDTA complex there is a strong pH dependence of both the intensity of the absorption and the stoichiometry of the complex suggesting that at pH values substantially greater than pKa a of EDTA (10.2) a 2 : 1 complex (2MV2+:...EDTA 4 -) is formed. At pH values significantly less than pKa 3 of EDTA a 1 : 1 complex is formed (MV2+... HEDTA 3 -). Photoexcitation of the complexes leads to the formation of reduced methyl viologen. The data draw attention to complications in previous model systems for the storage of solar energy.