as batteries and metal deposition. The liquids provide an
electrochemical window of about 2 V positive from the Zn/Zn2+
couple. Further details of the conductivity and electrochemical
properties are reported elsewhere.15
Having established that the cationic component can be varied
we have also investigated changing the metal-containing, i.e.
anionic, component. Heating choline chloride and SnCl2 in a
1+2 molar ratio provides a viscous liquid which has a freezing
range of 43–45 °C. The negative ion FAB mass spectrum shows
the presence of [SnCl3]2 and [Sn2Cl5]2; however, no higher
ions are observed in this case. For the tin-containing melts the
liquid formed from [YC2H4NMe3]Cl (Y = OC(O)Me) gave the
lowest melting point. Heating choline chloride+ZnCl2+SnCl2 in
a 1+1+1 molar ratio gives a liquid with a freezing point of
21–23 °C, i.e. similar to the pure zinc-containing melt but
significantly lower than the pure tin-containing one. The FAB
mass spectrum of this liquid shows the presence of the
individual metal-containing ions and the mixed metal ion
[SnZnCl5]2. Mixed metal melts allow the possibility of tuning
the catalytic properties of the liquids, as well as opening up
possibilities for electrodeposition of metal alloys.
To conclude, we have shown that heating functionalised
quaternary ammonium halides [Me3NC2H4Y]Cl and MCl2 (M
= Zn, Sn) gives materials that are conducting, viscous liquids at
or around room temperature. The freezing points are dependent
upon the symmetry of the cation and upon the nature of the
functionalised side chain. The advantages of these new ionic
liquids over presently available metal-containing ionic liquids
are that they are insensitive to moisture and are much cheaper
than imidazolium-based liquids. In addition, their Lewis acidity
can be altered by varying the metal chloride(s) used. The use of
these liquids as catalysts for the Diels–Alder reaction of
acroleins and dienes will be reported elsewhere.
We thank Scionix Ltd., a joint venture company between
Whyte Chemicals and the University of Leicester, for financial
support.