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Micellar effects on photoinduced redox reactions of Fe(bpy)2(CN)2 |
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| Authors: | Ott Horvth Kenneth L Stevenson |
| Institution: | a University of Veszprém, Department of General and Inorganic Chemistry, P.O. Box 158, H-8201 Veszprém Hungary b Indiana University-Purdue University of Fort Wayne, Department of Chemistry Fort Wayne, IN 46805 USA |
| Abstract: | Excitation of solutions of Fe(bipy)2(CN)2 by a 266-nm laser pulse produces a hydrated electron and the oxidized complex, Fe(bipy)2 (CN)2+, in the primary photochemical step, in homogeneous aqueous solution as well as in aqueous solutions containing cetyltrimethylammonium bromide (CTAB) or sodium dodecyl sulfate (SDS) micelles. In all cases nascent hydrated electrons react with ground state Fe(bipy)2(CN)2 to form Fe(bipy)2(CN)2?, and comparison of the decay constants in the three media (H2O: k = 2.8 × 1010 M?1 s?1; CTAB: k = 2.9 × 1010 M?1 s?1; SDS: k = 5.5 × 109 M?1 s?1), shows that the reaction is essentially unaffected by CTAB micelles but is much slower in SDS solution. Similar micellar effects were found for the back reaction between eaq? and Fe(bpy)2(CN)2+. Rate constants for the scavenging of the photogenerated hydrated electrons by methyl viologen (MV2+) cations and NO3? anions were measured in the three systems, and the results indicate that for scavenging by MV2+ the rate constants are decreased in the micelle systems (k in H2O, 8.4 × 1010; CTAB, 3.5 × 1010 and SDS, 1.58 × 1010 M?1 s?1), whereas for NO3? the CTAB micelle decreases while the SDS micelle enhances the scavenging compared to water solution (k in H2O, 8.3 × 109; CTAB, 7 × 108; and SDS, 2.05 × 1010 M?1 s?1). For the comproportionation reaction between Fe(bipy)2(CN)2+ and Fe(bipy)2(CN)2? both micelles reduce the rate (k in H2O, 3.3 × 1010; CTAB, 2.3 × 1010; and SDS, 1.05 × 1010 M?1s?1), but while the reaction of Fe(bipy)2(CN)2+ with MV+ is increased in CTAB compared to water, it is slowed in SDS (k in H2O, 2.4 × 1010; CTAB, 8.9 × 1010; and SDS, 1.8 × 1010 M?1s?1). All effects observed in these microheterogeneous systems can be uniformly interpreted in terms of Coulombic interactions between the actual reactants and the charged surface of the micelles. |
| Keywords: | Fe(bpy)2 (CN)2 Redox reactions Micellar effects |
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