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High-spin ground states via electron delocalization in mixed-valence imidazolate-bridged divanadium complexes

Nature Chemistry volume 2, pages 362368 (2010) | Download Citation

Abstract

The field of molecular magnetism has grown tremendously since the discovery of single-molecule magnets, but it remains centred around the superexchange mechanism. The possibility of instead using a double-exchange mechanism (based on electron delocalization rather than Heisenberg exchange through a non-magnetic bridge) presents a tantalizing prospect for synthesizing molecules with high-spin ground states that are well isolated in energy. We now demonstrate that magnetic double exchange can be sustained by simple imidazolate bridging ligands, known to be well suited for the construction of coordination clusters and solids. A series of mixed-valence molecules of the type [(PY5Me2)VII(µ-Lbr) VIII(PY5Me2)]4+ were synthesized and their electron delocalization probed through cyclic voltammetry and spectroelectrochemistry. Magnetic susceptibility data reveal a well-isolated S = 5/2 ground state arising from double exchange for [(PY5Me2)2V2(µ-5,6-dimethylbenzimidazolate)]4+. Combined modelling of the magnetic data and spectral analysis leads to an estimate of the double-exchange parameter of B = 220 cm−1 when vibronic coupling is taken into account.

  • Compound C12H12N2

    1,1-Bis(2-pyridyl)ethane

  • Compound C29H25N5

    2,6-Bis[1,1-bis(2-pyridyl)ethyl]pyridine

  • Compound C31H28I2N6V

    Acetonitrilo(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine) vanadium(II) diiodide

  • Compound C31H28F12N6P2V

    Acetonitrilo(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine) vanadium(II) bis(hexafluorophosphate)

  • Compound C4H5N2Na

    Sodium 2-methylimidazolate

  • Compound C15H11N2Na

    Sodium 4,5-diphenylimidazolate

  • Compound C7H5N2Na

    Sodium benzimidazolate

  • Compound C9H9N2Na

    Sodium 5,6-dimethylbenzimidazolate

  • Compound C61H53F18N12P3V2

    μ-Imidazolato-bis(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine)divanadium(II) tris(hexafluorophosphate)

  • Compound C62H55F18N12P3V2

    μ-2-Methylimidazolato-bis(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine)divanadium(II) tris(hexafluorophosphate)

  • Compound C61H52ClF18N12P3V2

    μ-2-Chloroimidazolato-bis(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine)divanadium(II) tris(hexafluorophosphate)

  • Compound C73H61F18N12P3V2

    μ-4,5-Diphenyimidazolato-bis(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine)divanadium(II) tris(hexafluorophosphate)

  • Compound C65H55F18N12P3V2

    μ-Benzimidazolato-bis(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine)divanadium(II) tris(hexafluorophosphate)

  • Compound C67H59F18N12P3V2

    μ-5,6-Dimethylbenzimidazolato-bis(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine)divanadium(II) tris(hexafluorophosphate)

  • Compound C67H59F24N12P4V2

    μ-5,6-DimethylbenzImidazolato-bis(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine)divanadium(II/III) tetrakis(hexafluorophosphate)

  • Compound C32H28F6N7PV+

    Imidazolato(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine) vanadium(II) hexafluorophosphate

  • Compound C36H30F6N7PV+

    Benzimidazolato(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine) vanadium(II) hexafluorophosphate

  • Compound C38H34F6N7PV+

    5,6-Dimethylbenzimidazolato(2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine) vanadium(II) hexafluorophosphate

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Acknowledgements

This research was funded by National Science Foundation (NSF) grant CHE-0617063. We thank the American–Australian Association and the 1851 Royal Commission for support of D.M.D. through postdoctoral fellowships, the Miller Research Foundation for providing a postdoctoral fellowship for D.M.J., and S. Baudron for preliminary experimental work and helpful discussions. The mass spectrometer was acquired with support from National Institutes of Health grant 1S10RR02239301, and C.P.K. acknowledges support through NSF grant CHE-0616279.

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  1. Department of Chemistry, University of California, Berkeley, California 94720-1460, USA

    • Bettina Bechlars
    • , Deanna M. D'Alessandro
    • , David M. Jenkins
    • , Anthony T. Iavarone
    •  & Jeffrey R. Long
  2. Department of Chemistry and Biochemistry, University of California, San Diego, California 92093-0332, USA

    • Starla D. Glover
    •  & Clifford P. Kubiak

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Contributions

B.B., D.M.D. and D.M.J. performed the majority of the experiments and data analysis. A.T.I. collected and analysed the mass spectrometry data. S.D.G. and C.P.K. assisted with acquisition of the FT-IR spectroelectrochemical data. J.R.L. designed and supervised the research. The paper was written by B.B., D.M.D. and J.R.L., and all authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Jeffrey R. Long.

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https://doi.org/10.1038/nchem.585

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