Multifunctional Ionic Liquids from Rhodium(I) Isocyanide Complexes: Thermochromic, Fluorescence, and Chemochromic...

Square-planar rhodium(I) isocyanide complexes exhibit unique chemical reactivities such as the formation of Rh-Rh bonds and oxidative addition. This paper details the syntheses and properties of multifunctional ionic liquids containing Rh^I isocyanide complexes [Rh(nBuNC)₄ ]X (X=Tf₂ N (=N(SO₂ CF₃ )₂^- ), Nf₂ N (=N(SO₂ C₄ F₉ )₂^- ), FSA (=N(SO₂ F)₂^- ), CF₃ BF₃^- ). Salts with Tf₂ N and Nf₂ N were liquids, whereas those with FSA and CF₃ BF₃ were solids at room temperature. The salts exhibited thermochromism in the liquid state, changing from orange at high temperatures to blue-purple at lower temperatures. This is based on the equilibrium between monomer, dimer, and other oligomers associated with Rh-Rh bond formation. The salts also exhibited fluorescence. Exposure of the Tf₂ N salt to methyl iodide vapor produced ionic liquid mixtures [Rh(nBuNC)₄ ]_x [Rh(nBuNC)₄ IMe]_(1-x) [Tf₂ N], concomitant with a color change from purple to red, orange, and yellow, extending the thermochromic color range. The reaction of the Tf₂ N salt and iodine produced mononuclear and polynuclear iodine adducts. Thus, these liquids exhibit thermochromism, fluorescence, vapochromism, chemical reactivities, and characteristic properties of ionic liquids.