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

Nature Chemistry volume 2, pages 362–368 (2010)Cite this article

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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.

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Figure 1: Double-exchange mechanism in mixed-valence manganites.
Figure 2: Synthesis of the pentapyridine ligand PY5Me2.
Figure 3: Crystal structure of the dinuclear complex [(PY5Me2)2V2(µ-5,6-dmbzim)]3+ in 14·3.5MeCN·Et2O.
Figure 4: Electrochemical and spectroscopic characterization of the imidazolate-bridged divanadium complexes.
Figure 5: Variable-temperature magnetic susceptibility data.
Figure 6: Spin-state energy diagrams and adiabatic potentials under the influence of vibronic coupling.

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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, 94720-1460, California, 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, 92093-0332, California, 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.

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Correspondence to Jeffrey R. Long.

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Bechlars, B., D'Alessandro, D., Jenkins, D. et al. High-spin ground states via electron delocalization in mixed-valence imidazolate-bridged divanadium complexes. Nature Chem 2, 362–368 (2010). https://doi.org/10.1038/nchem.585

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