Haris AMIR1, John HOLBREY1, Gosia SWADZBA-KWASNY1
1QUILL Research Centre, Belfast, United Kingdom
Ionic liquids containing borate anions have a long history; from tetraalkylborates1 through tetrafluoroborates2 to orthoborate anions,3 and most recently a range of functionalised cyanoborate systems.4 Here we describe studies exploring the expansion of the range of available orthoborate anions suitable for forming ionic liquids through transformation from tetra-oxo (B{OOOO}) into mixed oxygen/nitrogen (B{OONN}) and ultimately to tetraamine (B{NNNN}) coordination environments.
The coordinative stability of 4-coordinate borate anions incorporating common O- and novel N/O-, N-donor ligands (Fig. 1) were examined via NMR spectroscopy as solutions of their alkali metal salts (Li+, Na+, and K+) in D2O.
Ionic liquid salts were generated and characterised with 1?butyl?3?methylimidazolium ([C4mim]+) trihexyltetradecylphosphonium ([P66614]+) cations from hydrolytically stable anions, as identified from the NMR screening and the Gutmann donor numbers as a measure of relative basicity of the anions in their ionic liquid form was determined by 23Na NMR spectroscopy. Thermogravimetric analysis and differential scanning calorimetry confirm the thermal stability of new borate anions containing the B{OONN} and B{NNNN} core. Anion identities were confirmed, in the solid state, through single crystal XRD of tetrabutylphosphonium ([P4444]+) salts where the high level of cation symmetry promotes crystallisation. Ongoing characterisation and application of these new ionic liquid anions will be reported.