Hydrogen Bonding in the Crystal Structures of New Imidazolium Triflimide Protic Ionic Liquids

Abstract

The synthesis and crystal structures of 1,3-diamino-2-methylimidazolium bis(trifluoromethylsulfonyl)imide (1), 1,3-dihydroxy-2-methylimidazolium bis(trifluoromethylsulfonyl)imide (2) and 1-(2-(diethylammonio)ethyl)-3-methylimidazolium bis(bis(trifluoromethylsulfonyl)imide) (4) are reported. The salts 1, 2 and 4 have melting points below 100 °C, the intermediate 1-(2-(diethylamino)ethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (3) is liquid at room temperature. Compound 1 is monoclinic, space group P21/n with a = 8.4979(4) A, b = 12.2803(6) A, c = 13.9400(7) A, β = 93.086(4)°, and Z = 4. Compound 2 is monoclinic, space group P21/c with a = 7.6165(2) A, b = 20.5323(8) A, c = 9.7654(3) A, β = 111.046(2)°, and Z = 4. Compound 4 is triclinic, space group $$ P\overline{1} $$ with a = 8.5313(4) A, b = 9.2157(4) A, c = 20.5812(8) A, α = 84.668(2)°, β = 83.738(2)°, γ = 63.096(2)°, and Z = 2. The ions in 1 build a network of N–H···O hydrogen bonds, in 2 they are linked to chains by O–H···N and bifurcated O–H···O hydrogen bonds, whereas in 4 they form pairs by N–H···O contacts. The triflimide anions adopt transoid conformations. Short interionic contacts, conformational flexibility, and disorder phenomena were identified in the crystal structures of three new, low-melting, protic imidazolium triflimides.