Effects of ring tilting on rates of intramolecular electron transfer in mixed-valence 1′,2′, 1?,2?-tetraethyl-, l′,3′,1?,3?-tetraethyl-, and 1′,2′,1?,4?-hexaethylbiferrocenium triiodides

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Title:	Effects of ring tilting on rates of intramolecular electron transfer in mixed-valence 1′,2′, 1?,2?-tetraethyl-, l′,3′,1?,3?-tetraethyl-, and 1′,2′,1?,4?-hexaethylbiferrocenium triiodides
Authors:	Dong, T.-Y.a, Huang, C.-H.ab, Chang, C.-K.ac, Wen, Y.-S.a, Lee, S.-L.a, Chen, J.-A.a, Yeh, W.-Y.b, Yeh, A.c
Contributors:	Department of Chemistry, Tunghai University
Date:	1993
Issue Date:	2013-05-14T09:01:46Z (UTC)
Abstract:	Relatively minor perturbations caused by Cp ring substituents in a series of mixed-valence biferrocenium cations have pronounced effects on the electronic structure and rate of intramolecular electron transfer. The X-ray structure of 1′,2′,1?,2?-tetraethylbiferrocene has been determined at 298 K: C2/c, a = 18.760(3) ?, b = 9.568(3) ?, c=16.441 (3) ?, β = 130.494(13)°, Z = 4, Dcalcd =1.42 g cm-1, Rf = 0.038, and Rwf = 0.041. The isomeric compound 1′,3′,1?,3?,-tetraethylbiferrocene crystallizes in the triclinic space group P1? with one molecule in a unit cell with dimensions a = 5.8649(6) ?, b = 8.8462(6) ?, c = 12.4822(11) ?, α = 109.814(6)°, β= 103.063(8)°, and γ = 83.476(6)°; Rf = 0.046, and Rwf = 0.055. The mixed-valence compound 1′,3′,1?,3?,-tetraethylbiferrocenium triiodide crystallizes in the triclinic space group P1? with one molecule in a unit cell with dimensions a = 8.4567(20) ?, b = 9.0268(15) ?, c = 10.9182(12) ?, α = 105.777(12)°, β= 101.606(13)°, and γ = 106.301(15)°; Rf = 0.042, and Rwf = 0.042. A three-dimensional hydrogen bonding network is clearly found between the Cp ring hydrogen atoms and iodine counterion atoms. The two crystallographically equivalent metallocene moieties of the cation have dimensions intermediate between those of FeII and FeIII metallocenes. The variable-temperature 57Fe M?ssbauer data indicate that there is a pronounced dependency on sample history for 1′,1?-diethyl-, 1′,2′,1?,2?-tetraethyl-, and 1′,3′,1?,3?-tetraethylbiferrocenium triiodides. Crystalline samples of 1′,2′,1?,2?-tetraethyl- and 1′,3′,1?,3?-tetraethylbiferrocenium triiodide are delocalized on the M?ssbauer time scale in the solid state above 195 and 125 K, respectively. We suggest that the difference in the rates of electron transfer in the series of mixed-valence biferrocenium salts is a result of difference in the degree of tilting of the Cp rings from the parallel geometry. Deviations of the Cp rings from the parallel position were found to correlate quite well with the critical temperature for electronic delocalization-localization in mixed-valence biferrocenium salts. Based on extended H?ckel MO calculations, a theoretical explanation of the influence of bending back the Cp rings on the electron-transfer rates is also presented.
Relation:	Journal of the American Chemical Society Volume 115, Issue 14, 1993, Pages 6357-6368
Appears in Collections:	[Department of Chemistry ] Periodical Articles

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