Hard X-ray-Induced Valence Tautomeric Interconversion in Cobalt-o-Dioxolene Complexes

Thiago Francisco, William Gee, Helena Shepherd, Mark R. Warren, David A. Shultz, Paul R. Raithby, Carlos B. Pinherio

Research output: Contribution to journalArticle

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Abstract

Valence tautomers (VT) are electronically labile compounds showing charge transfer between redox-active ligands and a metal center. In cobalt bis(dioxolene)-type valence tautomers, the intramolecular metal-ligand electron transfer is accompanied by a change of metal ion spin state. The valence tautomeric interconversion (VTI) is a reversible process that creates two switchable electronic states (redox isomers). A low temperature, 30 – 100 K, single-crystal X-ray study of the [Co(diox)2(4-CN-py)2]·benzene complex (1) (diox = 3,5-di-t-butylsemiquinonate, (SQ•-) and/or 3,5-di-t-butylcatecholate (Cat2-) radical; 4-CN-py = 4-cyano-pyridine) using hard synchrotron X-ray radiation (0.48590Å) shows the formation of a remarkable, metastable, X-ray induced hs-[Co2+(SQ•-)2] valence tautomer at 30 K. As the temperature is raised the percentage of the hs-Co2+ isomer reduces from 80% to 13% at 60 K. At 100 K only the ls-[Co3+(SQ•-)(Cat2-)] is observed. As has been observed previously, between 150 - 290 K a non-cooperative hs-[Co2+(SQ•-)2] → ls-[Co3+(SQ•-)(Cat2-)] interconversion occurs in which pure hs-Co2+ state is found above 290 K. Fast cooling of the samples from 100 K to 30 K followed by illumination with white light and attenuated hard X-rays beam radiation exposition also induced ca. 80% molar fraction conversion from the ground state [Co3+(SQ•-)(Cat2-)] form to the metastable hs-[Co2+(SQ•-)2] tautomer. The actual mole fraction of the metastable hs-[Co2+(SQ•-)2] form is reduced upon warming, because of the thermally activated relaxation to the electronic ls-[Co3+(SQ•-)(Cat2-)] ground state. 1 is the first valence tautomer displaying metastable mole fraction interconversion at low temperatures as a direct result of the X-ray radiation used in a single-crystal, synchrotron-based, X-ray diffraction experiment.
Original languageEnglish
Pages (from-to)4774-4778
Number of pages5
JournalJournal of Physical Chemistry Letters
Volume8
Issue number19
DOIs
Publication statusPublished - 5 Oct 2017

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Cobalt
X rays
Synchrotrons
Radiation
Isomers
Ground state
Metals
Ligands
Single crystals
Electronic states
Benzene
Pyridine
Temperature
Metal ions
Charge transfer
Lighting
Cooling
X ray diffraction
Electrons
Experiments

Keywords

  • Valence tautomerism
  • Synchrotron radiation

Cite this

Hard X-ray-Induced Valence Tautomeric Interconversion in Cobalt-o-Dioxolene Complexes. / Francisco, Thiago; Gee, William; Shepherd, Helena; Warren, Mark R.; Shultz, David A.; Raithby, Paul R.; Pinherio, Carlos B.

In: Journal of Physical Chemistry Letters, Vol. 8, No. 19, 05.10.2017, p. 4774-4778.

Research output: Contribution to journalArticle

Francisco, Thiago ; Gee, William ; Shepherd, Helena ; Warren, Mark R. ; Shultz, David A. ; Raithby, Paul R. ; Pinherio, Carlos B. / Hard X-ray-Induced Valence Tautomeric Interconversion in Cobalt-o-Dioxolene Complexes. In: Journal of Physical Chemistry Letters. 2017 ; Vol. 8, No. 19. pp. 4774-4778.
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AU - Francisco, Thiago

AU - Gee, William

AU - Shepherd, Helena

AU - Warren, Mark R.

AU - Shultz, David A.

AU - Raithby, Paul R.

AU - Pinherio, Carlos B.

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N2 - Valence tautomers (VT) are electronically labile compounds showing charge transfer between redox-active ligands and a metal center. In cobalt bis(dioxolene)-type valence tautomers, the intramolecular metal-ligand electron transfer is accompanied by a change of metal ion spin state. The valence tautomeric interconversion (VTI) is a reversible process that creates two switchable electronic states (redox isomers). A low temperature, 30 – 100 K, single-crystal X-ray study of the [Co(diox)2(4-CN-py)2]·benzene complex (1) (diox = 3,5-di-t-butylsemiquinonate, (SQ•-) and/or 3,5-di-t-butylcatecholate (Cat2-) radical; 4-CN-py = 4-cyano-pyridine) using hard synchrotron X-ray radiation (0.48590Å) shows the formation of a remarkable, metastable, X-ray induced hs-[Co2+(SQ•-)2] valence tautomer at 30 K. As the temperature is raised the percentage of the hs-Co2+ isomer reduces from 80% to 13% at 60 K. At 100 K only the ls-[Co3+(SQ•-)(Cat2-)] is observed. As has been observed previously, between 150 - 290 K a non-cooperative hs-[Co2+(SQ•-)2] → ls-[Co3+(SQ•-)(Cat2-)] interconversion occurs in which pure hs-Co2+ state is found above 290 K. Fast cooling of the samples from 100 K to 30 K followed by illumination with white light and attenuated hard X-rays beam radiation exposition also induced ca. 80% molar fraction conversion from the ground state [Co3+(SQ•-)(Cat2-)] form to the metastable hs-[Co2+(SQ•-)2] tautomer. The actual mole fraction of the metastable hs-[Co2+(SQ•-)2] form is reduced upon warming, because of the thermally activated relaxation to the electronic ls-[Co3+(SQ•-)(Cat2-)] ground state. 1 is the first valence tautomer displaying metastable mole fraction interconversion at low temperatures as a direct result of the X-ray radiation used in a single-crystal, synchrotron-based, X-ray diffraction experiment.

AB - Valence tautomers (VT) are electronically labile compounds showing charge transfer between redox-active ligands and a metal center. In cobalt bis(dioxolene)-type valence tautomers, the intramolecular metal-ligand electron transfer is accompanied by a change of metal ion spin state. The valence tautomeric interconversion (VTI) is a reversible process that creates two switchable electronic states (redox isomers). A low temperature, 30 – 100 K, single-crystal X-ray study of the [Co(diox)2(4-CN-py)2]·benzene complex (1) (diox = 3,5-di-t-butylsemiquinonate, (SQ•-) and/or 3,5-di-t-butylcatecholate (Cat2-) radical; 4-CN-py = 4-cyano-pyridine) using hard synchrotron X-ray radiation (0.48590Å) shows the formation of a remarkable, metastable, X-ray induced hs-[Co2+(SQ•-)2] valence tautomer at 30 K. As the temperature is raised the percentage of the hs-Co2+ isomer reduces from 80% to 13% at 60 K. At 100 K only the ls-[Co3+(SQ•-)(Cat2-)] is observed. As has been observed previously, between 150 - 290 K a non-cooperative hs-[Co2+(SQ•-)2] → ls-[Co3+(SQ•-)(Cat2-)] interconversion occurs in which pure hs-Co2+ state is found above 290 K. Fast cooling of the samples from 100 K to 30 K followed by illumination with white light and attenuated hard X-rays beam radiation exposition also induced ca. 80% molar fraction conversion from the ground state [Co3+(SQ•-)(Cat2-)] form to the metastable hs-[Co2+(SQ•-)2] tautomer. The actual mole fraction of the metastable hs-[Co2+(SQ•-)2] form is reduced upon warming, because of the thermally activated relaxation to the electronic ls-[Co3+(SQ•-)(Cat2-)] ground state. 1 is the first valence tautomer displaying metastable mole fraction interconversion at low temperatures as a direct result of the X-ray radiation used in a single-crystal, synchrotron-based, X-ray diffraction experiment.

KW - Valence tautomerism

KW - Synchrotron radiation

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M3 - Article

VL - 8

SP - 4774

EP - 4778

JO - Journal of Physical Chemistry Letters

JF - Journal of Physical Chemistry Letters

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