Pronounced effect of substituents on the intramolecular electron-transfer rates in mixed-valence biferrocenium triiodide complexes

Dong, Teng Yuan; Schei, Chi Chang; Hwang, Ming Yhu; Lee, Ting Yu; Yeh, Show Kei; Wen, Yuh Sheng

doi:10.1021/om00038a012

Cited by 55 publications

(47 citation statements)

References 3 publications

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“…The ESR parameters are consistent with a small degree of delocalization of the odd electron in the MV 2(PF 6 ) and 3(PF 6 ) at 66 K. Indeed, for MV compounds of a homogeneous series, the anisotropy of the g -tensor (Δ g = g 1 – g 3 ) decreases as the rate of the intramolecular electron transfer increases . This property has been verified without exception in several cases in the Cp*(dppe)Fe series. ,,, The Δ g value is less than 0.01% smaller in 2(PF 6 ) than in 3(PF 6 ) but 220% larger in 2(PF 6 ) than in 1(PF 6 ) .…”

Section: Resultssupporting

confidence: 62%

Double Insertion of Thiophene Rings in Polyynediyl Chains to Stabilize Nanoscaled Molecular Wires with [Cp*(dppe)Fe] Termini

et al. 2016

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International audienceThe dinuclear iron complexes [Cp*(dppe)Fe-C C C4H2S-(C C)(x)-C4H2S-C C-Fe(dppe)Cp*] (2, x = 1; 3 x = 2) and [Cp*(dppe)Fe-C C-C4H2S-C C-C C-Fe(dppe) Cp*] (4) were prepared in one -pot procedures from known organometallic precursors. Compound 2 was obtained from Cp,*(dppe)Fe-C C-C4H2S-C C-C4H2S-C CH (6) and Cp*(dppe)FeCl (5) in 74% yield. Its relative 3, isolated in 84%, resulted from the oxidative coupling of Cp*(dppe)Fe-C C-C4H2S-C CH (7) in the presence of Cu(OAc)(2) and 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU). Complex 4 was obtained from the bridging ligand 2,5-bis(trimethylsilylbutadiynyl)thiophene (8) and two equiv of 5. The new complexes were characterized by ESI-mass spectrometry, IR, multi-nuclear NMR, cyclic voltammetry, and Mossbauer spectroscopy. Complex 3 was also analyzed by X-ray diffraction on a single crystal. The data are consistent with a sizable metal metal interaction across the 14- and 16 -carbon atoms of the bridges. The singly and doubly oxidized forms 2(PF6)(n) and 3(PF6)(n) (n = 1, 2) were obtained by oxidation of the corresponding 18 -electron iron(II) precursors with 1 and 2 equivs of ferrocenium salt, while 4 decomposed very quickly upon oxidation. The thermally stable salts 2(PF6)(n) and 3(PF6)(n) (n = 1, 2) were subjected to analyses by ESI-mass spectrometry, IR, Mossbauer, ESR, UV-vis, and NIR spectroscopies. The radical cations 2(PF6) and 3(PF6) belong to Class II of the mixed-valence Robin and Day classification with quite sizable electronic coupling parameters for large metal-metal separation (2(PF6), H-ab = 262 cm(-1), d(FeFe) = 17.7 angstrom; 3(PF6), H-ab = 203 cm(-1), d(FeFe) = 19.7 angstrom). Paramagnetic H-1 NMR spectroscopy was also performed on the dicationic salts to measure the magnetic exchange between the distant spin carriers (2(PF6)(2), Delta G(ST) = -120 cm(-1)). The data were analyzed with the support of quantum chemistry calculations at the DFT level of theory

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Section: Resultssupporting

confidence: 62%

Double Insertion of Thiophene Rings in Polyynediyl Chains to Stabilize Nanoscaled Molecular Wires with [Cp*(dppe)Fe] Termini

et al. 2016

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“…The rich chemistry of bridged mixed-valence dimers, especially those of ruthenium dimers and biferrocenium cations, − has captured considerable attention. Studies on these mixed-valence compounds have concentrated on the extent of electron delocalization, the shape of the corresponding intervalence transfer (IT) band, and the role of the bridge in the electron-transfer process.…”

Section: Introductionmentioning

confidence: 99%

Pronounced Effects of Ring Tilting on Rates of Intramolecular Electron Transfer in Polyalkyl-Substituted Mixed-Valence Biferrocenium Triiodides

et al. 1997

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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 structures of 1‘,2‘,1‘‘‘,2‘‘‘-tetrapropylbiferrocene, 1‘,2‘,1‘‘‘,2‘‘‘-tetrabenzylbiferrocene, 1‘,3‘,1‘‘‘,3‘‘‘-tetrapropylbiferrocene, 1‘,3‘,1‘‘‘,3‘‘‘-tetrabenzylbiferrocene, and their corresponding mixed-valence biferrocenium triiodide salts have been determined at 298 K. The rates of intramolecular electron transfer in the mixed-valence cations were estimated by variable-temperature 57Fe Mössbauer spectroscopy (time scale ∼107 s-1). The features in all of the 80 K spectra include two doublets, one with a quadrupole splitting (ΔE Q) of ∼2 mm s-1 (Fe(II) site) and the other with ΔE Q = ∼0.6 mm s-1 (Fe(III) site). This pattern of two doublets is expected for a mixed-valence biferrocenium cation which is valence-trapped on the time scale of the Mössbauer experiment (electron-transfer rate < ∼107 s-1 in the solid state). Increasing the sample temperature in 1‘,2‘,1‘‘‘,2‘‘‘-tetrapropylbiferrocenium triiodide, 1‘,2‘,1‘‘‘,2‘‘‘-tetrabenzylbiferrocenium triiodide, and 1‘,3‘,1‘‘‘,3‘‘‘-tetrabenzylbiferrocenium triiodide causes the two doublets to move together with no discernible line broadening, eventually becoming a single “average-valence” doublet at temperatures of 295, 265, and 190 K, respectively. In the case of 1‘,3‘,1‘‘‘,3‘‘‘-tetrapropylbiferrocenium triiodide, the two doublets at low temperatures do not coalesce into an average-valence doublet at 300 K (electron-transfer rate < ∼10 s-1 at 300 K). Thus, the micromodification of the relative positions of the alkyl substituents and the nature of the alkyl substituents has a dramatic influence on the rate of intramolecular electron transfer. The deviations of the Cp rings from the parallel position correlate quite well with the Mössbauer critical temperature for electronic delocalization−localization in mixed-valence cations. Qualitatively, we suggest that the metal nonbonding orbitals (d x 2 - y 2 , d xy ) start to interact with the ligand π orbitals as the Cp rings tilt from the parallel position. On the basis of the density functional calculations, a theoretical explanation of the influence of bending back the Cp rings on the electron-transfer rates is presented. The electrochemical measurements, IR data, and near-IR spectra for these mixed-valence biferrocenium cations are also presented.

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“…57 Fe Mo ¨ssbauer measurements were made on a constant-velocity instrument which has been previously described [25]. The absolute temperature accuracy is estimated to be 9/1 K, while the relative precision is 9/ 0.5 K. Computer fitting of the 57 Fe Mo ¨ssbauer data to Lorentzian lines were carried out with a modified version of a program previously reported [29].…”

Section: Physical Methodsmentioning

confidence: 99%

Pronounced effects of grinding on rates of intramolecular electron transfer in mixed-valence 1′,2′,1‴,2‴-tetranaphthylmethyl- and 1′,3′,1‴,3‴-tetranaphthylmethyl-biferrocenium triiodides

Dong

Lin

Lee

et al. 2003

Journal of Organometallic Chemistry

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Pronounced effect of substituents on the intramolecular electron-transfer rates in mixed-valence biferrocenium triiodide complexes

Cited by 55 publications

References 3 publications

Double Insertion of Thiophene Rings in Polyynediyl Chains to Stabilize Nanoscaled Molecular Wires with [Cp*(dppe)Fe] Termini

Double Insertion of Thiophene Rings in Polyynediyl Chains to Stabilize Nanoscaled Molecular Wires with [Cp*(dppe)Fe] Termini

Pronounced Effects of Ring Tilting on Rates of Intramolecular Electron Transfer in Polyalkyl-Substituted Mixed-Valence Biferrocenium Triiodides

Pronounced effects of grinding on rates of intramolecular electron transfer in mixed-valence 1′,2′,1‴,2‴-tetranaphthylmethyl- and 1′,3′,1‴,3‴-tetranaphthylmethyl-biferrocenium triiodides

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