Electron delocalization in mixed-valence biferrocenium salts: nuclear magnetic resonance contact shift studies

Dong, Teng Yuan; Hwang, Ming Yhu; Hsu, Tsui Ling; Schei, Chi Chang; Yeh, Show Kei

doi:10.1021/ic00326a017

Cited by 17 publications

(10 citation statements)

References 2 publications

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“…All crystallographically characterized biferrocenes ( 5 , 6 , 7 , 9 ) in this study feature common characteristics. As found in many other biferrocenes, − the two ferrocene units are arranged in a transoid manner with the Cp1···Cp2···Cp3···Cp4 torsion angle being around 180° (Table , Cp denotes the centroid of the respective Cp ring). The two connected Cp rings in the Cp−Cp moiety are practically coplanar (Table , C7−C6−C11−C12), with C6−C7 distances of 1.46−1.47 Å, typical for C(sp 2 )−C(sp 2 ) single bonds.…”

Section: Resultsmentioning

confidence: 86%

“…This indicates trapped Fe II and Fe III sites at 295 K on the M€ ossbauer time scale; that is, the ET rate is below 10 7 s -1 . [62][63][64][65][66][67][68][69][70] The electron transfer in solution within mixed-valent BFca derivatives is studied at 300 K. In order to gain insight into the primary oxidation event, 7 is treated with substoichiometric amounts of iodine in CDCl 3 and 1 H NMR spectra are recorded (Figure 13). 26 Resonances associated with the C-terminal ferrocene (H2a/H5a, H3a/H4a, H7a/H10a, H8a/H9a) are essentially undisturbed, while resonances of the N-terminal ferrocene unit (H2/H5, H3/H4, H7/H10, H8/ H9) are paramagnetically broadened and shifted to higher frequency.…”

Section: Resultsmentioning

confidence: 99%

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Biferrocene Amino Acid, a Ferrocenylogoue of Ferrocene Amino Acid: Synthesis, Cross-Linking, and Redox Chemistry

et al. 2010

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Access of the novel biferrocene amino acid 7 is provided by two different routes, namely, via desymmetrization of a biferrocene and via palladium-catalyzed cross-coupling of two substituted ferrocenes. The dissymmetric biferrocene 7 is head−head coupled to ureylene-bridged bis(biferrocene) 9 and also head−tail coupled to amide-bridged bis(biferrocene) 14. The monomer 7 and the dimers 9 and 14 are oxidized to mixed-valent cations 7 + , 9 + , 9 2+ , and 14 2+ . The valencies are trapped in the solid state as shown by Mössbauer and EPR spectroscopy and by X-ray diffraction analysis of [7](I 3 ). Paramagnetic NMR shift studies (7 → 7 + ) suggest that the hole is localized at the N-substituted ferrocene unit [BocNH-{III}-{II}-COOMe]+. According to DFT calculations and individual redox potentials, the dications 9 2+ and 14 2+ are best described as [MeOOC-{II}-{III}-NHCONH-{III}-{II}-COOMe]2+ and [BocNH-{III}-{II}-CONH-{III}-{II}-COOMe]2+ valence isomers, respectively. The interaction between neighboring ferrocene/ferrocenium sites in the mixed-valent systems is determined by Hush analyses of the NIR intervalence bands. The extent depends on the bridge type (direct link, amide, ureylene) and the zero-point difference of the individual redox-active units.

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Section: Resultsmentioning

confidence: 86%

Section: Resultsmentioning

confidence: 99%

Biferrocene Amino Acid, a Ferrocenylogoue of Ferrocene Amino Acid: Synthesis, Cross-Linking, and Redox Chemistry

et al. 2010

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“…Paramagnetic 1 H NMR spectroscopy was used to identify the localization of the ferrocenium site in 2 + . [11][12][13][14][15] Upon titration of 2 with substoichiometric amounts of iodine only resonances of protons H 13 , H 14 and H 15 (Scheme 1, ESI †) are affected suggesting spin density at the non-hydrogen bonded iron site. This is fully confirmed by DFT calculations on 2 + showing spin density at the non-hydrogen bonded iron site (FeÁ Á ÁN distance 3.54 Å; FeÁ Á ÁH distance 2.66 Å; Fig.…”

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confidence: 99%

Diferrocenyl tosyl hydrazone with an ultrastrong NH⋯Fe hydrogen bond as double click switch

et al. 2015

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“…It has been reported that the unpaired electron in the Fe(III) ion would lead to negative spin density and positive contact shifts at the cyclopentadienyl protons. For example, three broad peaks at 16.38, 20.24, and 21.65 ppm were observed for biferrocenium triiodide . Our magnetic measurements (SQUID) for 9 and 12 also indicate the presence of the Fe(II) oxidation state.…”

Section: Resultsmentioning

confidence: 56%

Redox-Switched Bonding in Biferrocene-Containing Crown Ethers: Complexing Behavior

et al. 1999

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Two series of novel biferrocenes containing crown ethers have been prepared. The new compounds include 1‘,1‘ ‘‘-bis(1,4,7,10,13-pentaoxa-16-azacyclooctadecane-16-methyl)biferrocene (7) and 1‘,1‘ ‘‘-bis(1,4,7,10-tetraoxa-13-azacyclopentadecane-13-methyl)biferrocene (8). The complexing behavior toward alkali and alkaline earth metal cations for 7 and 8 was investigated. Solid-state structures have been determined for NaPF6 and KPF6 complexes of 8. The reaction products of 7 and 1-(1,4,7,10,13-pentaoxa-16-azacyclooctadecane-16-methyl)ferrocene with I2 have also been characterized by structural determinations, 1H NMR, magnetic measurements, and 57Fe Mössbauer technique. Complexation properties for 7 and 8 have been assessed by use of 1H NMR, cyclic voltammetry measurements, and 57Fe Mössbauer analyses. When the system was studied by cyclic voltammetry, new redox couples were observed in the presence of certain alkaline earth metal cations. For example, the electrochemical behavior observed for 8 with Ba2+ ion is fundamentally different since two new redox couples are observed for Ba2+ concentrations within the range 0 < [Ba2+] < 2equiv. The peak currents for the two new redox couples increase with the concentration of Ba2+ ion until a full equivalent is added; at this point, the original redox couples disappear and the new redox couples reach full development. This is quite unusual since compounds 7 and 8 do not have a well-formed cavity to facilitate the formation of internal metal cation complexes. Furthermore, the Mössbauer and UV/vis studies suggest no direct interaction between the iron atom and metal cation. The solid-state electron transfer in mixed-valence 1‘,1‘ ‘‘-bis(crown ether)biferrocenium cations was also characterized by Mössbauer spectroscopy. The features in all of the Mössbauer spectra include two doublets, one with a quadrupole splitting (ΔE Q) of ∼2.2 mms-1 (Fe(II) site) and the other with ΔE Q = ∼0.4 mms-1 (Fe(III) site). The Mössbauer studies indicate that the electron-transfer rates in the series of mixed-valence 1‘,1‘ ‘‘-bis(crown ether)biferrocenium cations are less than 107 s-1 in the solid state.

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Electron delocalization in mixed-valence biferrocenium salts: nuclear magnetic resonance contact shift studies

Cited by 17 publications

References 2 publications

Biferrocene Amino Acid, a Ferrocenylogoue of Ferrocene Amino Acid: Synthesis, Cross-Linking, and Redox Chemistry

Biferrocene Amino Acid, a Ferrocenylogoue of Ferrocene Amino Acid: Synthesis, Cross-Linking, and Redox Chemistry

Diferrocenyl tosyl hydrazone with an ultrastrong NH⋯Fe hydrogen bond as double click switch

Redox-Switched Bonding in Biferrocene-Containing Crown Ethers: Complexing Behavior

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