An Ionic Liquid State Composed of Superoxide Radical Anions and Crownether-Coordinated Potassium Cations. Issue 8 (1st January 2017)

• Record Type: Journal Article
• Authors: Kitada, Atsushi; Ishikawa, Daisuke; Fukami, Kazuhiro; Murase, Kuniaki
• Is Part Of: Journal of the Electrochemical Society. Volume 164:Issue 8(2017)
• Page Start: H5119
• Page End: H5123
• Publication Date: 2017-01-01
• Subjects: crownether -- ionic liquid -- phase separation -- radical -- superoxide; Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/2.0131708jes
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : We report an "ionic liquid state" substance composed of superoxide radical anions (O2 − ) and crownether-coordinated potassium cations. A binary mixture of 18-crown-6-ether (18C6) and potassium superoxide (KO2 ) becomes liquid above ca. 38°C. The coordination of 18C6 to K + and the presence of O2 − were confirmed in the liquid state by Raman spectroscopy measurements. Below 38°C, however, the 18C6-KO2 mixture does not form a complex but undergoes phase separation to parent phases of solid 18C6 and KO2, because the ion-dipole interaction between K + and 18C6 is overwhelmed by the ion-ion interaction between K + and O2 − . In other words, the pair of O2 − and 18C6-coordinated K + only appears above the melting point of pure 18C6, to form an "ionic liquid state". Among radical-containing ionic liquids, the liquid 18C6-KO2 mixture has high fluidity and comparable conductivity. The findings show stabilization of superoxide radical anions at liquid state with high concentration, which could be used for many radical reactions.