[Bis(imidazolyl)-BH2 ]+ [Bis(triazolyl)-BH2 ]- Ionic Liquids with High Density and Energy Capacity.

[Bis(imidazolyl)-BH2 ]+ [bis(triazolyl)-BH2 ]- and [bis(imidazolyl)-BH2 ]+ [tris(triazolyl)-BH]- were synthesized, the cations and anions of which were functionalized with B-H groups and azoles. As B-H groups contribute to the hypergolic activity and azole groups improve the energy output, the resulting ionic liquids exhibited ignition delay times as low as 20 ms and energy outputs as high as 461.1 kJ mol-1 . In addition, densities (1.07-1.22 g cm-3 ) and density-specific impulse (≈360 s g cm-3 ) values reached a relatively high level. These ionic liquids show great promise as sustainable rocket fuels.