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Caption : figure s1. asymmetric unit of the fe3 grid at 100k. hydrogen atoms are omitted for clarity.

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Caption : figure s2. thermal ellipsoid plot (50% of probability) for fe3 at 100k. hydrogen atoms are omitted for clarity.

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Caption : figure s3. packing of molecules down crystallographic ‘a’ axis. hydrogen atoms are omitted for clarity.

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Caption : figure s4. packing of molecules down crystallographic ‘b’ axis. hydrogen atoms are omitted for clarity.

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Caption : figure s5. packing of molecules down crystallographic ‘c’ axis. hydrogen atoms are omitted for clarity.

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Caption : figure s6. thermal ellipsoid plot (50% of probability) for fe3 for the -500ps data. hydrogen atoms are omitted for clarity.

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Caption : figure s7. thermal ellipsoid plot (50% of probability) for fe3 for the 200pss data. hydrogen atoms are omitted for clarity.

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Caption : figure s8. thermal ellipsoid plot (50% of probability) for fe3 for the 500ps data. hydrogen atoms are omitted for clarity.

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Caption : figure s9. thermal ellipsoid plot (50% of probability) for fe3 for the 800ps data. hydrogen atoms are omitted for clarity.

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Caption : figure s10. thermal ellipsoid plot (50% of probability) for fe3 for the 1ns data. hydrogen atoms are omitted for clarity.

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Caption : figure s11. environment of feii ions and definition of the θ angle and the angular distortion parameter (θ).2,3

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Caption : figure s12. photowilson plots of fe3.

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Caption : figure s13. molecular representation of the [fe3l4]4+ grid at different temperatures, showing the rotation of the pyridine ring and the nearest acetonitrile molecule refined as disordered over two positions.