Mechanisms of iodide-triiodide exchange reactions in ionic liquids: A reactive molecular-dynamics exploration

BYRNE, AARON; BRINGA, EDUARDO M.; DEL PÓPOLO, MARIO G.; KOHANOFF, JORGE J.; GALASSI, VANESA; ENGLISH, NIALL J.

International Journal of Molecular Sciences

MDPI AG

Año: 2019 vol. 20 p. 1123 - 1137

1661-6596

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 (I − )-to-triiodide (I 3 − ) exchange reactions, we have performed 10 ns reactive molecular-dynamics calculations in the liquid state for 1-butyl-3-methylimidazolium iodide ([BMIM][I]) 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 ~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.