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On the Mechanism of the Iodide–Triiodide Exchange Reaction in a Solid-State Ionic Liquid

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journal contribution
posted on 21.06.2017, 18:45 by Joás Grossi, Jorge J. Kohanoff, Niall J. English, Eduardo M. Bringa, Mario G. Del Pópolo
Efficient charge transport has been observed in iodide-based room-temperature ionic liquids when doped with iodine. To investigate preferred pathways for the iodide (I)-to-triiodide (I3) exchange reaction and to clarify the origin of this high ionic conductivity, we have conducted electronic structure calculations in the crystal state of 1-butyl-3-methylimidazolium iodide ([BMIM]­[I]). Energy barriers for the different stages of the iodine-swapping process, including the reorientation of the I···I3 moiety, were determined from minimum energy paths as a function of a reaction coordinate. Hirshfeld charges and structural parameters, such as bond lengths and angles, were monitored during the reaction. Several bond-exchange events were observed with energy barriers ranging from 0.17 to 0.48 eV and coinciding with the formation of a twisted I···I3 complex. Striking similarities were observed in the mechanics and energetics of this charge-transfer process in relation to solid-state superionic conductors.