Hydrogen Bonding in Ionic Liquids

Professor Patricia Hunt - School of Chemical and Physical Sciences

Ionic liquids (ILs) are new solvents and electrolytes, composed of discrete cations and anions. IL differ from typical salts in that the ions are larger, more diffuse and chemically complex. A key feature of ILs is the ability to tailor the physico-chemical properties by varying the constituent ions. ILs are being explored for an astonishingly wide range of applications, including for use in industry, in energy applications, in technological devices and for health applications. However, advances are being hampered by an inability to predict, or even rationalise, IL properties.

Hydrogen bonding (H-bonding) is present in many ILs and plays a key role in determining the physico-chemical properties. The versatility of ILs is, in-part, due to the diverse range of H-bonding that occurs within ILs. While the general nature of a simple "ordinary" H-bond is well known, a deeper characterisation of even traditional H-bonds is more complex. ILs also exhibit a fundamentally distinct and new type of H-bond, the doubly ionic H-bond, a H-bond between two ions, overshadowed by ionic interactions, but also enhanced by the strong polarization of a charged environment.

Computational (quantum chemical) studies can provide insight into the molecular level interactions within ILs, thus establishing a link between the constituent ions and the resultant physico-chemical properties. In this presentation I will interrogate, through computational methods, the structural, vibrational and electronic characteristics of H-bonds in ILs. I will highlight the non-traditional features of H-bonding exhibited by ILs and explore how to conceptualise H-bonding within ILs.