Pressure versus temperature effects on intramolecular electron transfer in mixed-valence complexes

Stephan Scheins, Jacob Overgaard, Grigore A. Timco, Adam Stash, Yu Sheng Chen, Finn K. Larsen, Mogens Christensen, Mads R.V. Jørgensen, Solveig R. Madsen, Mette S. Schmøkel, Bo B. Iversen

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    Abstract

    Mixed-valence trinuclear carboxylates, [M3O(O 2CR)6L3] (M=metal, L=terminal ligand), have small differences in potential energy between the configurations M IIMIIIMIII⇔ MIIIM IIMIII⇔MIIIMIIIMII, which means that small external changes can have large structural effects, owing to the differences in coordination geometry between M2+ and M 3+ sites (e.g., about 0.2 Å for Fe-O bond lengths). It is well-established that the electron transfer (ET) between the metal sites in these mixed-valence molecules is strongly dependent on temperature and on the specific crystal environment; however, herein, for the first time, we examine the effect of pressure on the electron transfer. Based on single-crystal X-ray diffraction data that were measured at 15, 90, 100, 110, 130, 160, and 298 K on three different crystals, we first unexpectedly found that our batch of Fe 3O (O2CC(CH3)3)6(C 5H5N)3 (1) exhibited a different temperature dependence of the ET process than previous studies of compound 1 have shown. We observed a phase transition at around 130 K that was related to complete valence trapping and Hirshfeld surface analysis revealed that this phase transition was governed by a subtle competition between C-H⋯pi; and π⋯pi; intermolecular interactions. Subsequent high-pressure single-crystal X-ray diffraction at pressures of 0.15, 0.35, 0.45, 0.74, and 0.96 GPa revealed that it was not possible to trigger the phase transition (i.e., valence trapping) by a reduction of the unit-cell volume, owing to this external pressure. We conclude that modulation of the ET process requires anisotropic changes in the intermolecular interactions, which occur when various directional chemical bonds are affected differently by changes in temperature, but not by the application of pressure.

    Original languageEnglish
    Pages (from-to)195-205
    Number of pages11
    JournalChemistry - A European Journal
    Volume19
    Issue number1
    DOIs
    Publication statusPublished - 2 Jan 2013

    Keywords

    • carboxylates
    • electron transfer
    • high-pressure diffraction
    • mixed-valent compounds
    • X-ray diffraction

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    • CCDC 908208: Experimental Crystal Structure Determination

      Scheins, S. (Creator), Overgaard, J. (Creator), Timco, G. (Creator), Stash, A. (Creator), Chen, Y. S. (Creator), Larsen, F. K. (Creator), Christensen, M. (Creator), Jørgensen, M. R. V. (Creator), Madsen, S. R. (Creator), Schmøkel, M. S. (Creator) & Iversen, B. B. (Creator), Cambridge Crystallographic Data Centre, 28 Jun 2013

      Dataset

    • CCDC 908217: Experimental Crystal Structure Determination

      Scheins, S. (Creator), Overgaard, J. (Creator), Timco, G. (Creator), Stash, A. (Creator), Chen, Y. S. (Creator), Larsen, F. K. (Creator), Christensen, M. (Creator), Jørgensen, M. R. V. (Creator), Madsen, S. R. (Creator), Schmøkel, M. S. (Creator) & Iversen, B. B. (Creator), Cambridge Crystallographic Data Centre, 29 Oct 2012

      Dataset

    • CCDC 908210: Experimental Crystal Structure Determination

      Scheins, S. (Creator), Overgaard, J. (Creator), Timco, G. (Creator), Timco, G. (Creator), Chen, Y. S. (Creator), Larsen, F. K. (Creator), Christensen, M. (Creator), Jørgensen, M. R. V. (Creator), Madsen, S. R. (Creator), Schmøkel, M. S. (Creator) & Iversen, B. B. (Creator), Cambridge Crystallographic Data Centre, 28 Jun 2013

      Dataset

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