Thermal Properties and Solvent Polarities of Mixed-Valence Ionic Liquids Containing Cationic Biferrocenylene Derivatives

Ionic liquids (ILs) containing cationic mixed-valence biferrocenylene derivatives were synthesized with an octanoyl or octyl substituent in each cation. Their melting pointsranged between 25 and 39 degrees C, and the octanoyl derivatives exhibited higher melting points thanthe octyl derivatives. In addition, each IL exhibited a glass transition in the temperature rangingfrom-66 to-45 degrees C after melting. Their melting points were similar to 10 degrees C higher than those ofmononuclear octamethylferrocenium salts bearing the same substituents. The solvent polarity(ETN) and Kamlet-Taft parameters (pi*,alpha, and beta) of these dinuclear and mononuclear ILswere then examined. The dinuclear ILs bearing octanoyl substituents exhibited significantincreases inETNand pi*and a decrease in alpha with the decreasing temperature, whereas the otherILs exhibited a significantly less pronounced temperature dependence. Finally, the intervalence charge-transfer (or charge-resonance) bands of the octanoyl dinuclear ILs exhibited red shifts with the decreasing temperature, which can be regarded as self-thermosolvatochromism

Automated summary

Ionic liquids containing cationic mixed-valence biferrocenylene derivatives were synthesized, and their melting points and temperature dependence were found to be related to the substituents on the cations.