Spectroscopic and electrochemical properties of europium(III) ion in hydrophobic ionic liquids under controlled condition of water content

Nagaishi, Ryuji ; Arisaka, Makoto ; Kimura, Takaumi ; Kitatsuji, Yoshihiro  

In order to elucidate coordination states of europium(III) ion in ionic liquids (ILs) and its physicochemical behavior, spectroscopic and electrochemical properties of Eu(III) were studied as a function of water content in hydrophobic ILs consisting of anion (bis(trifluoromethanesulfonyl)imide = tfsi) and cation (imidazolium or ammonium). The luminescence studies indicate that Eu(III) acts spectroscopically as aqua complex in the water-saturated ILs giving 9 of the inner-sphere hydration number of Eu(III), and that at the hydration number 9 tfsi anion involves in asymmetry of the coordination sphere of Eu(III) and in the quenching of photo-excited Eu(III). The electrochemical studies show that the divalent Eu(II) is more stable in the IL than in aqueous solution, and that the motion of Eu(III) is inhibited effectively by the matrix of IL.