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Chemistry. 2017 Jan 18;23(4):823-831. doi: 10.1002/chem.201604420. Epub 2016 Dec 5.

Thermochromic Magnetic Ionic Liquids from Cationic Nickel(II) Complexes Exhibiting Intramolecular Coordination Equilibrium.

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Department of Chemistry, Graduate School of Science, Kobe University, Rokkodai, Nada, Kobe, Hyogo, 657-8501, Japan.
Department of Applied Chemistry, Faculty of Engineering, Tokyo University of Science, Yamaguchi, Sanyo-Onoda, Yamaguchi , 756-0884, Japan.
Center for Supports to Research and Education Activities, Kobe University, Kobe, Hyogo, 657-8501, Japan.
Department of Physics, Graduate School of Science, Kobe University, Kobe, Hyogo, 657-8501, Japan.
Molecular Photoscience Research Center, Kobe University, Kobe, Hyogo, 657-8501, Japan.


Among the various thermochromic materials, liquid thermochromic materials are comparatively rare. To produce functional thermochromic liquids, we have designed ionic liquids based on cationic nickel complexes with ether side chains, [Ni(acac)(Me2 NC2 H4 NR1 R2 )]Tf2 N ([1]Tf2 N: R1 =C3 H6 OEt, R2 =Me; [2]Tf2 N: R1 =C3 H6 OMe, R2 =Me; [3]Tf2 N: R1 =R2 =C3 H6 OMe), where acac=acetylacetonate and Tf2 N=(F3 CSO2 )2 N- . The side chains (R1 , R2 ) can moderately coordinate to the metal center, enabling temperature-dependent coordination equilibria in the liquid state. [1]Tf2 N is a liquid at room temperature. [2]Tf2 N is obtained as a solid (Tm =352.7 K) but remains liquid at room temperature after melting. [3]Tf2 N is a solid with a high melting point (Tm =422.3 K). These salts display thermochromism in the liquid state, appearing red at high temperatures and orange, light-blue, or bluish-green at lower temperatures, and exhibiting concomitant changes in their magnetic properties. This phenomenon is based on temperature-dependent equilibrium between a square-planar diamagnetic species and a paramagnetic species with intramolecular ether coordination.


chelates; ionic liquids; magnetic properties; thermal properties; thermochromism


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