Molecular states of water in room temperature ionic liquidsElectronic Supplementary Information available. See http://www.rsc.org/suppdata/cp/b1/b106900d/

ATR and transmission IR spectroscopy have been used to investigate the state of water in room temperature ionic liquids (RTILs) based on the 1-alkyl-3-methylimidazolium cation with the anions: PF6−, SbF6−, BF4−, ClO4−, CF3SO3−, (CF3SO2)2N−, NO3− and CF3CO2−. It has been shown that in these RTILs water molecules absorbed from the air are present mostly in the “free” (not self-associated) state, bound via H-bonding with PF6−, BF4−, SbF6−, ClO4−, CF3SO3−, (CF3SO2)2N− with the concentrations of dissolved water in the range 0.2–1.0 mol dm−3. It has been concluded that most of the water molecules at these concentrations exist in symmetric 1 : 2 type H-bonded complexes: anion...HOH...anion. Additional evidence that the preferred sites of interaction with water molecules are the anions has been obtained from the experiments with RTILs of the 1-butyl-2,3-dimethylimidazolium and 1-butyl-2,3,4,5-tetramethylimidazolium cations. Water molecules can also form associated liquid-like formations in RTILs with anions of stronger basicity such as NO3− and CF3CO2−. When these RTILs are exposed to air the water concentrations exceed 1.0 mol dm−3. The strength of H-bonding between water molecules and anions increases in the order PF6− < SbF6− < BF4− < (CF3SO2)2N− < ClO4− < CF3SO3− < NO3− < CF3CO2−. The energies of this H-bonding were estimated from spectral shifts, with the resulting enthalpies being in the range 8–13 kJ mol−1. ATR-IR spectroscopy has also been used to study H-bonding between methanol and RTILs.