Conductivity and Redox Potentials of Ionic Liquid Trihalogen Monoanions [X(3)](−), [XY(2)](−), and [BrF(4)](−) (X=Cl, Br, I and Y=Cl, Br)

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)](−)).