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http://140.128.103.80:8080/handle/310901/21091
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| Title: | 4-and 3-hydroxypyridine complexes of pentacyanoferrate(II, III) |
| Authors: | Chen, C.-N.a, Wu, M.-C.a, Yeh, A.a, Tsai, T.Y.R. |
| Contributors: | Department of Chemistry, Tunghai University |
| Keywords: | Electrochemistry;Hydroxypyridine complexes;Kinetics and mechanism;Pentacyanoferrate complexes |
| Date: | 1998 |
| Issue Date: | 2013-05-14T09:01:37Z (UTC)
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| Abstract: | A series of Fe(CN) 5L 3- complexes, where L=4-, 3-hydroxypyridines and 4-, 3-methoxypyridines, was prepared in aqueous solution by the reaction of Fe(CN) 5OH 2 3- with excess ligand. A metal-to-ligand charge-transfer transition was observed for the complexes at 414 (4-hydroxypyridine), 363 (3-hydroxypyridine), 336 (4-methoxypyridine) and 368 nm (3-methoxypyridine). The corresponding Fe(III) complexes also display a ligand-to-metal charge-transfer band at 565 (4-hydroxypyridine), 503 (3-hydroxypyridine), 440 (4-methoxypyridine) and 530 nm (3-methoxypyridine). Cyclic voltammetry of the complexes under study has shown that the oxidation is a one-electron reversible process with E 1/2 values of 0.40 (4-hydroxypyridine), 0.45 (3-hydroxypyridine), 0.43 (4-methoxypyridine) and 0.45 V (3-methoxypyridine) versus NHE at 25 °C, μ=0.10 M (LiClO 4) and pH=5 (acetate). The rate constants of formation and dissociation of the Fe(CN) 5L 3- complexes were measured and the k f and k d values (25 °C, μ=0.1 M (LiClO 4), pH=5) are 0.273 M -1 s -1 and 1.08 × 10 -3 s -1 (4-hydroxypyridine), 171 M -1 s -1 and 2.28 × 10 -3 S -1 (3-hydroxypyridine), 375 M -1 s -1 and 2.05 × 10 -3 s -1 (4-methoxypyridine), 421 M -1 s -1 and 2.37 × 10 -3 s -1 (3-methoxypyridine). The k f value of the 4-hydroxypyridine complex is three orders of magnitude smaller than that of the other complexes under investigation. The difference may arise from the favorable tautomeric equilibrium of the 4-hydroxypyridine ligand to its keto-form rather than via a different reaction mechanism. By comparing the k f results of complexes of 4-, 3-methoxy-pyridines and 4-, 3-hydroxypyridines, the equilibrium constants of tautomerization of hydroxypyridines towards their keto-isomers can be estimated, and the values are 1310 and 1.4 for 4-and 3-hydroxypyridines, respectively. ? 1998 Elsevier Science S.A. |
| Relation: | Inorganica Chimica Acta
Volume 267, Issue 1, 3 January 1998, Pages 81-86 |
| Appears in Collections: | [化學系所] 期刊論文
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