Solvent-dependent modulation of metal-metal electronic interactions in a dinuclear cyanoruthenate complex: A detailed electrochemical, spectroscopic and computational study

Ashley B. Wragg; Sofia Derossi; Timothy L. Easun; Michael W. George; Xue Zhong Sun; František Hartl; Alexander H. Shelton; Anthony J.H.M. Meijer; Michael D. Ward

doi:10.1039/c2dt31001e

Solvent-dependent modulation of metal-metal electronic interactions in a dinuclear cyanoruthenate complex: A detailed electrochemical, spectroscopic and computational study

Ashley B. Wragg, Sofia Derossi, Timothy L. Easun, Michael W. George, Xue Zhong Sun, František Hartl, Alexander H. Shelton, Anthony J.H.M. Meijer, Michael D. Ward

Research output: Journal Publication › Article › peer-review

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Abstract

The dinuclear complex [{Ru(CN) ₄} ₂(μ-bppz)] ^4- shows a strongly solvent-dependent metal-metal electronic interaction which allows the mixed-valence state to be switched from class 2 to class 3 by changing solvent from water to CH ₂Cl ₂. In CH ₂Cl ₂ the separation between the successive Ru(ii)/Ru(iii) redox couples is 350 mV and the IVCT band (from the UV/Vis/NIR spectroelectrochemistry) is characteristic of a borderline class II/III or class III mixed valence state. In water, the redox separation is only 110 mV and the much broader IVCT transition is characteristic of a class II mixed-valence state. This is consistent with the observation that raising and lowering the energy of the d(π) orbitals in CH ₂Cl ₂ or water, respectively, will decrease or increase the energy gap to the LUMO of the bppz bridging ligand, which provides the delocalisation pathway via electron-transfer. IR spectroelectrochemistry could only be carried out successfully in CH ₂Cl ₂ and revealed class III mixed-valence behaviour on the fast IR timescale. In contrast to this, time-resolved IR spectroscopy showed that the MLCT excited state, which is formulated as Ru ^III(bppz ^-)Ru ^II and can therefore be considered as a mixed-valence Ru(ii)/Ru(iii) complex with an intermediate bridging radical anion ligand, is localised on the IR timescale with spectroscopically distinct Ru(ii) and Ru(iii) termini. This is because the necessary electron-transfer via the bppz ligand is more difficult because of the additional electron on bppz ^- which raises the orbital through which electron exchange occurs in energy. DFT calculations reproduce the electronic spectra of the complex in all three Ru(ii)/Ru(ii), Ru(ii)/Ru(iii) and Ru(iii)/Ru(iii) calculations in both water and CH ₂Cl ₂ well as long as an explicit allowance is made for the presence of water molecules hydrogen-bonded to the cyanides in the model used. They also reproduce the excited-state IR spectra of both [Ru(CN) ₄(μ-bppz)] ^2- and [{Ru(CN) ₄} ₂(μ-bppz)] ^4- very well in both solvents. The reorganization of the water solvent shell indicates a possible dynamical reason for the longer life time of the triplet state in water compared to CH ₂Cl ₂.

Original language	English
Pages (from-to)	10354-10371
Number of pages	18
Journal	Dalton Transactions
Volume	41
Issue number	34
DOIs	https://doi.org/10.1039/c2dt31001e
Publication status	Published - 14 Sept 2012
Externally published	Yes

ASJC Scopus subject areas

Inorganic Chemistry

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Wragg, A. B., Derossi, S., Easun, T. L., George, M. W., Sun, X. Z., Hartl, F., Shelton, A. H., Meijer, A. J. H. M., & Ward, M. D. (2012). Solvent-dependent modulation of metal-metal electronic interactions in a dinuclear cyanoruthenate complex: A detailed electrochemical, spectroscopic and computational study. Dalton Transactions, 41(34), 10354-10371. https://doi.org/10.1039/c2dt31001e

@article{57e2b89b13584c58acb2e4bad3ccd21d,

title = "Solvent-dependent modulation of metal-metal electronic interactions in a dinuclear cyanoruthenate complex: A detailed electrochemical, spectroscopic and computational study",

abstract = "The dinuclear complex [{Ru(CN) 4} 2(μ-bppz)] 4- shows a strongly solvent-dependent metal-metal electronic interaction which allows the mixed-valence state to be switched from class 2 to class 3 by changing solvent from water to CH 2Cl 2. In CH 2Cl 2 the separation between the successive Ru(ii)/Ru(iii) redox couples is 350 mV and the IVCT band (from the UV/Vis/NIR spectroelectrochemistry) is characteristic of a borderline class II/III or class III mixed valence state. In water, the redox separation is only 110 mV and the much broader IVCT transition is characteristic of a class II mixed-valence state. This is consistent with the observation that raising and lowering the energy of the d(π) orbitals in CH 2Cl 2 or water, respectively, will decrease or increase the energy gap to the LUMO of the bppz bridging ligand, which provides the delocalisation pathway via electron-transfer. IR spectroelectrochemistry could only be carried out successfully in CH 2Cl 2 and revealed class III mixed-valence behaviour on the fast IR timescale. In contrast to this, time-resolved IR spectroscopy showed that the MLCT excited state, which is formulated as Ru III(bppz -)Ru II and can therefore be considered as a mixed-valence Ru(ii)/Ru(iii) complex with an intermediate bridging radical anion ligand, is localised on the IR timescale with spectroscopically distinct Ru(ii) and Ru(iii) termini. This is because the necessary electron-transfer via the bppz ligand is more difficult because of the additional electron on bppz - which raises the orbital through which electron exchange occurs in energy. DFT calculations reproduce the electronic spectra of the complex in all three Ru(ii)/Ru(ii), Ru(ii)/Ru(iii) and Ru(iii)/Ru(iii) calculations in both water and CH 2Cl 2 well as long as an explicit allowance is made for the presence of water molecules hydrogen-bonded to the cyanides in the model used. They also reproduce the excited-state IR spectra of both [Ru(CN) 4(μ-bppz)] 2- and [{Ru(CN) 4} 2(μ-bppz)] 4- very well in both solvents. The reorganization of the water solvent shell indicates a possible dynamical reason for the longer life time of the triplet state in water compared to CH 2Cl 2.",

author = "Wragg, {Ashley B.} and Sofia Derossi and Easun, {Timothy L.} and George, {Michael W.} and Sun, {Xue Zhong} and Franti{\v s}ek Hartl and Shelton, {Alexander H.} and Meijer, {Anthony J.H.M.} and Ward, {Michael D.}",

year = "2012",

month = sep,

day = "14",

doi = "10.1039/c2dt31001e",

language = "English",

volume = "41",

pages = "10354--10371",

journal = "Dalton Transactions",

issn = "1477-9226",

publisher = "Royal Society of Chemistry",

number = "34",

}

Wragg, AB, Derossi, S, Easun, TL, George, MW, Sun, XZ, Hartl, F, Shelton, AH, Meijer, AJHM & Ward, MD 2012, 'Solvent-dependent modulation of metal-metal electronic interactions in a dinuclear cyanoruthenate complex: A detailed electrochemical, spectroscopic and computational study', Dalton Transactions, vol. 41, no. 34, pp. 10354-10371. https://doi.org/10.1039/c2dt31001e

TY - JOUR

T1 - Solvent-dependent modulation of metal-metal electronic interactions in a dinuclear cyanoruthenate complex

T2 - A detailed electrochemical, spectroscopic and computational study

AU - Wragg, Ashley B.

AU - Derossi, Sofia

AU - Easun, Timothy L.

AU - George, Michael W.

AU - Sun, Xue Zhong

AU - Hartl, František

AU - Shelton, Alexander H.

AU - Meijer, Anthony J.H.M.

AU - Ward, Michael D.

PY - 2012/9/14

Y1 - 2012/9/14

N2 - The dinuclear complex [{Ru(CN) 4} 2(μ-bppz)] 4- shows a strongly solvent-dependent metal-metal electronic interaction which allows the mixed-valence state to be switched from class 2 to class 3 by changing solvent from water to CH 2Cl 2. In CH 2Cl 2 the separation between the successive Ru(ii)/Ru(iii) redox couples is 350 mV and the IVCT band (from the UV/Vis/NIR spectroelectrochemistry) is characteristic of a borderline class II/III or class III mixed valence state. In water, the redox separation is only 110 mV and the much broader IVCT transition is characteristic of a class II mixed-valence state. This is consistent with the observation that raising and lowering the energy of the d(π) orbitals in CH 2Cl 2 or water, respectively, will decrease or increase the energy gap to the LUMO of the bppz bridging ligand, which provides the delocalisation pathway via electron-transfer. IR spectroelectrochemistry could only be carried out successfully in CH 2Cl 2 and revealed class III mixed-valence behaviour on the fast IR timescale. In contrast to this, time-resolved IR spectroscopy showed that the MLCT excited state, which is formulated as Ru III(bppz -)Ru II and can therefore be considered as a mixed-valence Ru(ii)/Ru(iii) complex with an intermediate bridging radical anion ligand, is localised on the IR timescale with spectroscopically distinct Ru(ii) and Ru(iii) termini. This is because the necessary electron-transfer via the bppz ligand is more difficult because of the additional electron on bppz - which raises the orbital through which electron exchange occurs in energy. DFT calculations reproduce the electronic spectra of the complex in all three Ru(ii)/Ru(ii), Ru(ii)/Ru(iii) and Ru(iii)/Ru(iii) calculations in both water and CH 2Cl 2 well as long as an explicit allowance is made for the presence of water molecules hydrogen-bonded to the cyanides in the model used. They also reproduce the excited-state IR spectra of both [Ru(CN) 4(μ-bppz)] 2- and [{Ru(CN) 4} 2(μ-bppz)] 4- very well in both solvents. The reorganization of the water solvent shell indicates a possible dynamical reason for the longer life time of the triplet state in water compared to CH 2Cl 2.

AB - The dinuclear complex [{Ru(CN) 4} 2(μ-bppz)] 4- shows a strongly solvent-dependent metal-metal electronic interaction which allows the mixed-valence state to be switched from class 2 to class 3 by changing solvent from water to CH 2Cl 2. In CH 2Cl 2 the separation between the successive Ru(ii)/Ru(iii) redox couples is 350 mV and the IVCT band (from the UV/Vis/NIR spectroelectrochemistry) is characteristic of a borderline class II/III or class III mixed valence state. In water, the redox separation is only 110 mV and the much broader IVCT transition is characteristic of a class II mixed-valence state. This is consistent with the observation that raising and lowering the energy of the d(π) orbitals in CH 2Cl 2 or water, respectively, will decrease or increase the energy gap to the LUMO of the bppz bridging ligand, which provides the delocalisation pathway via electron-transfer. IR spectroelectrochemistry could only be carried out successfully in CH 2Cl 2 and revealed class III mixed-valence behaviour on the fast IR timescale. In contrast to this, time-resolved IR spectroscopy showed that the MLCT excited state, which is formulated as Ru III(bppz -)Ru II and can therefore be considered as a mixed-valence Ru(ii)/Ru(iii) complex with an intermediate bridging radical anion ligand, is localised on the IR timescale with spectroscopically distinct Ru(ii) and Ru(iii) termini. This is because the necessary electron-transfer via the bppz ligand is more difficult because of the additional electron on bppz - which raises the orbital through which electron exchange occurs in energy. DFT calculations reproduce the electronic spectra of the complex in all three Ru(ii)/Ru(ii), Ru(ii)/Ru(iii) and Ru(iii)/Ru(iii) calculations in both water and CH 2Cl 2 well as long as an explicit allowance is made for the presence of water molecules hydrogen-bonded to the cyanides in the model used. They also reproduce the excited-state IR spectra of both [Ru(CN) 4(μ-bppz)] 2- and [{Ru(CN) 4} 2(μ-bppz)] 4- very well in both solvents. The reorganization of the water solvent shell indicates a possible dynamical reason for the longer life time of the triplet state in water compared to CH 2Cl 2.

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U2 - 10.1039/c2dt31001e

DO - 10.1039/c2dt31001e

M3 - Article

C2 - 22810117

AN - SCOPUS:84865013136

SN - 1477-9226

VL - 41

SP - 10354

EP - 10371

JO - Dalton Transactions

JF - Dalton Transactions

IS - 34

ER -

Solvent-dependent modulation of metal-metal electronic interactions in a dinuclear cyanoruthenate complex: A detailed electrochemical, spectroscopic and computational study

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