Hydrogen bonding of nanoconfined water in ionic liquids

1-Alkyl-3-methylimidazolium nitrate ([Cnmim][NO3], n = 4, 6, and 8)-D2O provided a small-angle neutron scattering (SANS) peak, representing D2O aggregations (Abe et al., J. Phys. Chem. Lett. 5 (2014)1175 and J. Mol. Liq. 346 (2022) 117035). Nanoconfined water (water pocket) appeared in the water-rich region, with a size distribution that was almost monodispersed. The water pocket in [C4mim][NO3] was characterized by the hydrogen bonding (Abe et al., J. Mol. Liq. 210 (2015) 200). In this work, the hydrogen bonding state of [Cnmim][NO3]-D2O (n = 2, 6, and 8) was examined by Raman spectroscopy. The water concentration dependencies of the OD stretching band of D2O indicated that the hydrogen bonding state of the water pocket was invariant. The hydrogen/deuteron (H/D) exchange reaction was observed only in [C6mim] [NO3]-D2O, with the H/D exchange completed within 1 h. Moreover, large pD values were observed only in [C6mim][NO3]-D2O, and the kinetic pD behavior supported the H/D exchange. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the hydrogen bonding state of alkyl-3-methylimidazolium nitrate-D2O and finds that the hydrogen bonding state of the water pocket remains unchanged under different concentrations, and the hydrogen/deuteron exchange reaction is observed only under specific conditions.