Conductivity and Redox Potentials of Ionic Liquid Trihalogen Monoanions [X₃]⁻, [XY₂]⁻, and [BrF₄]⁻ (X=Cl, Br, I and Y=Cl, Br)

Abstract

Abstract The ionic liquid (IL) trihalogen monoanions [N 2221 ][X 3 ] − and [N 2221 ][XY 2 ] − ([N 2221 ] + =triethylmethylammonium, X=Cl, Br, I, Y=Cl, Br) were investigated electrochemically via temperature dependent conductance and cyclic voltammetry (CV) measurements. The polyhalogen monoanions were measured both as neat salts and as double salts in 1‐butyl‐1‐methyl‐pyrrolidinium trifluoromethane‐sulfonate ([BMP][OTf], [X 3 ] − /[XY 2 ] − 0.5 M). Lighter IL trihalogen monoanions displayed higher conductivities than their heavier homologues, with [Cl 3 ] − being 1.1 and 3.7 times greater than [Br 3 ] − and [I 3 ] − , respectively. The addition of [BMP][OTf] reduced the conductivity significantly. Within the group of polyhalogen monoanions, the oxidation potential develops in the series [Cl 3 ] − >[BrCl 2 ] − >[Br 3 ] − >[IBr 2 ] − >[ICl 2 ] − >[I 3 ] − . The redox potential of the interhalogen monoanions was found to be primarily determined by the central halogen, I in [ICl 2 ] − and [IBr 2 ] − , and Br in [BrCl 2 ] − . Additionally, tetrafluorobromate(III) ([N 2221 ] + [BrF 4 ] − ) was analyzed via CV in MeCN at 0 °C, yielding a single reversible redox process ([BrF 2 ] − /[BrF 4 ] − ).