Ionic liquids containing the triply negatively charged tricyanomelaminate anion and a B(C₆F₅)₃ adduct anion

Abstract

Room-temperature ionic liquids containing the triply charged tricyanomelaminate (tcmel) ion [C(3)N(6)(CN)(3)](3-) were synthesized. The 1-methyl-3-methylimidazolium (MMIm), 1-ethyl-3-methylimidazolium (EMIm), and 1-butyl-3-methylimidazolium (BMIm) salts of the tricyanomelaminate ion have glass transition temperatures (-6, -20, and -30 °C) similar to those found for the analogous monomeric dicyanoamide salts. They are thermally stable up to over 200 °C and dissolve in polar organic solvents. Addition of B(C(6)F(5))(3) to M(3) [tcmel] (M=Na, MMIm, EMIm, BMIm) yields salts containing the very voluminous adduct ion [C(3)N(6) {CN·B(C(6)F(5))(3)}(3)](3-) (tcmel_3B). The solid-state structure of [MMIm](3-) [tcmel] shows only long cation···anion contacts but in large number, while the solid-state structure of [Na(THF)(3)](3-) [tcmel_3B]·1.76 THF displays strong interactions of the sodium cation with the amido nitrogen atoms of the anion. Hence this adduct anion cannot be regarded as a weakly coordinating anion. A similar situation is found for the MMIm salt, [MMIm](3) [tcmel_3B]·2.66 CH(2)Cl(2), in which weak hydrogen bonds with the acidic proton of the MMIm ion are observed. On the basis of computations the energetics, structural trends, and charge transfer of adduct anion formation were studied.