Structural and Theoretical Study of Salts of the [B9 H14 ]- Ion: Isolation of Multiple Isomers and Implications for Energy Storage.

Boranes and boron hydrides are well known for their novel molecular structures and useful chemical reactivity, with [B9 H14 ]- notable in particular for its ease of isolation, unusual structure, and tautomerization. We report an experimental and theoretical investigation of the structure of [B9 H14 ]- and the energetics of some of its reactions. Salts of [B9 H14 ]- with 1-ethyl-3-methylimidazolium and N-butyl-N-methylpyrrolidinium were characterized by single-crystal X-ray diffraction and demonstrate the stabilization of an isomer of [B9 H14 ]- not previously observed in the solid state. Heats of formation and acid dissociation constants of [B9 H14 ]- and closely related structures were calculated. The results suggest a mechanism for particularly energetic hypergolic ignition induced by protonation and suggest potential for reversible H2 storage. These results encourage further investigation of [B9 H14 ]- as an energy-storage medium in ionic systems.