Room-temperature ionic liquids containing the triply charged tricyanomelaminate (tcmel) ion [C3N6(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(C6F5)3 to M3[tcmel] (M=Na, MMIm, EMIm, BMIm) yields salts containing the very voluminous adduct ion [C3N6{CN⋅B(C6F5)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 CH2Cl2, 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.
Liquid despite containing trianions: 1-Ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium salts of the cyanomelaminate (tcmel) trianion [C3N6(CN)3]3− are room-temperature ionic liquids, while the analogous salts with the B(C6F5)3 adduct anion [C3N6{CN⋅B(C6F5)3}3]3− (tcmel_3B) have melting points above 100 °C. The picture shows the solid-state structure of [Na(THF)3]3[tcmel_3B]⋅1.76 THF (C gray, F light blue, N dark blue, Na yellow, P red; THF omitted).
Relevant to Brian Manor
No comments:
Post a Comment