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

Xue Lan; Tomoyuki Mochida; Yusuke Funasako; Kazuyuki Takahashi; Takahiro Sakurai; Hitoshi Ohta

doi:10.1002/chem.201604420

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

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

Authors

Xue Lan¹, Tomoyuki Mochida¹, Yusuke Funasako², Kazuyuki Takahashi¹, Takahiro Sakurai³, Hitoshi Ohta^{4

5}

Affiliations

¹ Department of Chemistry, Graduate School of Science, Kobe University, Rokkodai, Nada, Kobe, Hyogo, 657-8501, Japan.
² Department of Applied Chemistry, Faculty of Engineering, Tokyo University of Science, Yamaguchi, Sanyo-Onoda, Yamaguchi , 756-0884, Japan.
³ Center for Supports to Research and Education Activities, Kobe University, Kobe, Hyogo, 657-8501, Japan.
⁴ Department of Physics, Graduate School of Science, Kobe University, Kobe, Hyogo, 657-8501, Japan.
⁵ Molecular Photoscience Research Center, Kobe University, Kobe, Hyogo, 657-8501, Japan.

PMID: 27805277
DOI: 10.1002/chem.201604420

Abstract

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 (T_m =352.7 K) but remains liquid at room temperature after melting. [3]Tf₂ N is a solid with a high melting point (T_m =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.

Keywords: chelates; ionic liquids; magnetic properties; thermal properties; thermochromism.