Ionic liquids and deep eutectic solvents have engendered wide and increasing research
interest in recent years due to their interesting and tunable physical, chemical and
solvation properties. The addition of metal halide salts to ionic liquids and deep eutectic
solvents results in HMILs (halometallate ionic liquids) and HMDESs (halometallate deep
eutectic solvents). A detailed understanding of these systems is vital to develop a
relationship between chemical structure and properties which would enhance the useful
application of HMILs and HMDESs.
In this work bismuth based HMILs and nickel based HMDESs were studied via
DFT calculations. The aims of studying both systems were: to understand the speciation
in solution, and the driving forces determining speciation; to analyse the intermolecular
interactions present; and to investigate the electronic structure of the systems.
In the bismuth HMIL system the anionic speciation was elucidated; Cl{ , [BiCl4]{ ,
[BiCl5]2{ , [Bi2Cl7]{ , [Bi2Cl8]2{ , and [Bi2Cl9]3{ anions can be accessed by varying the
mole fraction of BiX3 added to the ionic liquid (X = Cl, Br, I). An associative halide
exchange mechanism was found, with a low barrier to reaction indicating that rapid
exchange of halide atoms is likely to occur in solution. Experimental valence band XPS
was reproduced, indicating that the theoretical method describes the electronic structure
of HMILs well.
In the nickel HMDES system speciation was found to be in
uenced by both
enthalpic and entropic factors. Highly charged complexes were enthalpically favoured
over neutral species due to stronger intermolecular interactions, including doubly ionic
hydrogen bonds. The previously reported thermochemical equilibrium between
octahedral (low temperature) and tetrahedral (high temperature) species was rationalised
via thermochemical analysis; the octahedral species is enthalpically favoured and the
tetrahedral species entropically favoured. As temperature is a factor in the entropic part
of Gibbs free energy the tetrahedral species becomes favoured at elevated temperatures.Open Acces
