Mechanisms of Iodide-Triiodide Exchange Reactions in Ionic Liquids: A Reactive Molecular-Dynamics Exploration

A Byrne and EM Bringa and MG Del Popolo and JJ Kohanoff and V Galassi and NJ English, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 20, 1123 (2019).

DOI: 10.3390/ijms20051123

Efficient charge transport has been observed in iodine-doped, iodide- based room-temperature ionic liquids, yielding high ionic conductivity. To elucidate preferred mechanistic pathways for the iodide exchange reactions, we have performed 10 ns reactive molecular-dynamics calculations in the liquid state for 1-butyl-3-methylimidazolium iodide (BMIMI) at 450 to 750 K. Energy-barrier distributions for the iodine-swapping process were determined as a function of temperature, employing a charge-reassignment scheme drawn in part from electronic- structure calculations. Bond-exchange events were observed with rate- determining energy barriers ranging from similar to 0.19 to 0.23 +/- 0.06 eV at 750 and 450 K, respectively, with an approximately Arrhenius temperature dependence for iodine self-diffusivity and reaction kinetics, although diffusion dominates/limits the bond-exchange events. This charge transfer is not dissimilar in energetics to those in solid- state superionic conductors.

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