Syntheses and crystal structures of two ionic liquids with halogen-bonding groups: 4,5-dibromo- and 4,5-diiodo-l-butyl-3-methylimidazolium trifluoromethanesulfonates

摘要

We have prepared and characterized two novel Lewis acidic ionic liquids, 4,5-dibromo- and 4,5-diiodo-l-butyl-3-methylimidazolium trifluoromethanesulfonates, using differential scanning calorimetry and single-crystal X-ray analysis. The effect of the halogen species on the phase transition behaviour and the cation-anion interacting geometry was investigated. The minor difference in chemical structure strongly affects the melting point, glass transition temperature and crystal structure because of the different halogen-bonding strength and linearity between C-Br··· O and C-I ···O. Both the salts melt above room temperature, but the fused salts show glass-forming property and poor crystallizability.