Edinburgh Research Archive >
Chemistry, School of >
Chemistry thesis and dissertation collection >
Please use this identifier to cite or link to this item:
|Title: ||Exploring gas-phase ionic liquid aggregates by mass spectrometry and computational chemistry|
|Authors: ||Gray, Andrew Peter|
|Supervisor(s): ||Campbell, Eleanor|
Camp, Philip J.
|Issue Date: ||22-Jun-2012|
|Publisher: ||The University of Edinburgh|
|Abstract: ||Ionic liquids (IL) are salts which are liquid at low temperatures, typically with
melting points under 100 °C. In recent years ILs have been treated as novel solvents
and used in a wide variety of applications such as analytical and separation
processes, electrochemical devices and chemical syntheses. The properties of many
ILs have been extensively studied; these studies have primarily focused on the
investigation of key physical properties including viscosity, density and solubility.
This thesis presents mass spectrometry (MS) and computational data to investigate
the intrinsic interactions between a small number of IL ions and also their
interactions with contaminants.
MS was used to study gas-phase aggregates of three ILs based on the 1-butyl-3-
methylimidazolium (C4mim+) cation. The influence of different ion sources was
investigated on C4mimCl. Conventional electrospray ionisation (ESI) and nano-ESI
techniques were compared with recently developed sonic-spray ionisation (SSI) and
plasma assisted desorption ionisation (PADI). SSI was found to be beneficial to the
formation of larger aggregates while PADI was significantly less efficient. Gas-phase
structures of the singly charged cationic aggregates of C4mimCl were characterised
with the aid of collision induced dissociation (CID) and density functional theory
(DFT) calculations. Additionally, CID and DFT gave consistent results for the
relative stability of the C4mimCl aggregates, showing a good agreement between
experiment and theory.
Mixed solutions of C4mimCl with a range of metal chloride salts were used to form
aggregates incorporating both IL and metal chlorides. LiCl, NaCl, KCl, CsCl, MgCl2
and ZnCl2 were all combined with C4mimCl. Magic number characteristics were
observed for a number of pure IL and mixed aggregates. Many of the mixed species
were characterised using MS and DFT calculations. In particular, the relative
stabilities were determined and the structures of the aggregates were calculated. It
was found that the metal ions would normally act as a core for the aggregates with
the stability determined by the metal-chlorine binding strength and the steric hindrance of the aggregates. It was necessary to exploit pseudopotentials as opposed
to all-electron basis sets for the larger aggregates and aggregates containing heavy
While water is a very effective contaminant for ILs it was not possible to observe
gas-phase IL aggregates incorporating this despite using multiple methods.
Additionally the presence of protonated aggregates was likewise not observed
throughout the range of experiments. Possible structures where these features would
be incorporated were studied with DFT to obtain some insight into their lack of
|Sponsor(s): ||Engineering and Physical Sciences Research Council (EPSRC)|
|Keywords: ||ionic liquid|
|Appears in Collections:||Chemistry thesis and dissertation collection|
Items in ERA are protected by copyright, with all rights reserved, unless otherwise indicated.