Modelling non−covalent interactions and thermal decomposition pathways in oxyanion−containing ionic liquids
File(s)
Author(s)
Becker, Julian
Type
Thesis
Abstract
Ionic Liquids (ILs) are versatile materials with applications in academia and industry. The choice of the constituent IL ions depends on the properties required for a specific application. Designing ILs to match application−specific requirements is an exciting but daunting idea due to the vast number of ion combinations and inter−ionic interaction modes. While an understanding of inter−ionic interactions has been developed for some selected ILs, there is a knowledge gap when other ions are considered.
This thesis aims to deepen the understanding of interactions in ILs. To this end, we performed density functional theory calculations on oxyanion−containing imidazolium ILs. The conformational space of the relevant ion pairs (IPs) was sampled, and the interactions present were analysed thoroughly. We demonstrate that electrostatics largely defines cation−anion attraction, while weaker interactions (e.g., dispersion and hydrogen bonding) can still be driving local structuring effects. The analysis is briefly extended to IP dimers, allowing for interactions between ions of like charge.
The perchlorate anion shows potential for unprecedented anion−anion attraction and forms energetic ILs with a tendency for exothermic decomposition. A variety of thermal perchlorate decomposition pathways leading to the formation of oxygen are modelled, and we demonstrate that anion−anion interactions may have a critical impact on the activation parameters of the thermal decomposition process.
Often, ILs are mixed/contaminated with charge−neutral molecular compounds. In a first step, we model the interactions present in ion−molecule heterodimers. The interaction strength strongly depends on the charge distribution of the charge−neutral molecule, and we provide a protocol to estimate the ion−molecule interaction strength from the electrostatic potential of the charge−neutral molecules. We briefly demonstrate how interactions change when the cation and the anion simultaneously interact with each other and with a charge−neutral molecule in an IP−molecule cluster.
This thesis aims to deepen the understanding of interactions in ILs. To this end, we performed density functional theory calculations on oxyanion−containing imidazolium ILs. The conformational space of the relevant ion pairs (IPs) was sampled, and the interactions present were analysed thoroughly. We demonstrate that electrostatics largely defines cation−anion attraction, while weaker interactions (e.g., dispersion and hydrogen bonding) can still be driving local structuring effects. The analysis is briefly extended to IP dimers, allowing for interactions between ions of like charge.
The perchlorate anion shows potential for unprecedented anion−anion attraction and forms energetic ILs with a tendency for exothermic decomposition. A variety of thermal perchlorate decomposition pathways leading to the formation of oxygen are modelled, and we demonstrate that anion−anion interactions may have a critical impact on the activation parameters of the thermal decomposition process.
Often, ILs are mixed/contaminated with charge−neutral molecular compounds. In a first step, we model the interactions present in ion−molecule heterodimers. The interaction strength strongly depends on the charge distribution of the charge−neutral molecule, and we provide a protocol to estimate the ion−molecule interaction strength from the electrostatic potential of the charge−neutral molecules. We briefly demonstrate how interactions change when the cation and the anion simultaneously interact with each other and with a charge−neutral molecule in an IP−molecule cluster.
Version
Open Access
Date Issued
2023-03
Date Awarded
2023-06
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Welton, Tom
Sponsor
Defence Science and Technology Laboratory (Great Britain)
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)