No abstract

New families of salts, based on quaternary ammonium, 1-methyl-3-alkylimidazolium or N-methyl-N-alkylpyrrolidinium organic cations together with the dicyanamide (dca, N(CN) 2 2 ) anion are reported. The salts are low melting compounds, all those reported are liquid at room temperature, for example 1-methyl-3-ethylimidazolium dicyanamide (mp 221 °C) and N-methyl-N-ethylpyrrolidinium dicyanamide (mp 210 °C). Some of the salts exhibit multiple crystalline phases below their melting points. Above their melting points they are stable to at least 200 °C. Many of the salts were found to be glass forming when cooled rapidly to 2100 °C. The room-temperature liquids exhibit very low viscosities, for example ethylmethylimidazolium dicyanamide: h = 21 cP at ambient temperature (25 °C).

No abstract

No abstract

The bis(trifluoromethanesulfonyl)amide, TFSA, anion is widely used in the genesis of room temperature ionic liquids as it is non-spherical, fluorinated and has a particularly diffuse charge. However, the extent to which each of these structural features is responsible for the low melting point, fluidity and excellent stability of the resultant ionic liquids has yet to be described. We present the synthesis and analysis of a range of analogous, non-fluorinated species containing the bis(methanesulfonyl)amide, NMes 2 À , ligand. Utilisation of this anion produces ionic liquids that are hydrophilic and extremely low melting, but with decreased thermal and electrical stability and significantly increased viscosity. The crystal structures of the dimethyl pyrrolidinium bis(methanesulfonyl)amide and TFSA species are compared, and the number of close contacts within each is assessed. Comparison of these structural and physical properties provides new insight into the effect of anion fluorination on these ionic liquids.

A new series of salts, based on the N-methyl-N-alkylpyrrolidinium cation and the PF 6 -anion, are reported and their thermal properties described for alkyl ) Me, Et, Pr, Bu, Hx, and Hp. X-ray structures of several of the salts are also reported. The N,N-dimethylpyrrolidinium hexafluorophosphate has a melting point greater than 390°C; however, the N-methyl-N-butylpyrrolidinium derivative melts at 70°C. Most of the PF 6 -salts were observed to have lower melting points in comparison with the analogous iodide salts. Most of the salts exhibit one or more thermal transitions prior to melting and a final entropy of melting less than 20 J K -1 mol -1 , behavior which has previously been associated with the formation of plastic crystal phases. Good crystal structure solutions were obtained at low temperatures in the case of the alkyl ) propyl and heptyl derivatives. The loss of diffraction peaks and changes in symmetry at higher temperatures indicated the presence of dynamic rotational disorder, supporting the understanding that the plastic properties arise from rotational motions in the crystal.

A range of low melting salts of the bis(trifluoromethanesulfonyl)amide (TFSA) anion with hindered organic cations (N-methyl-1-methylpyrrolinium, N,N-dimethylpyrrolidinium, N,N,N,-trimethylammonium, and N,N,N,N-tetrakis(n-propyl)ammonium) have been crystallized. Single-crystal X-ray diffraction data show these materials to consist of discrete ions with only weak C−H···O (or for Me3NH N−H···O) contacts between the constituent atoms of the cations and anions close to the limits of van der Waals separations. Consequently, the observed physical properties of these materials presumably result from the diffuse negative charge on the TFSA anion and inefficient packing of these large and irregularly shaped ions.

No abstract