Structural and Theoretical Study of Salts of the [B₉H₁₄]⁻ Ion: Isolation of Multiple Isomers and Implications for Energy Storage

Abstract

Boranes and boron hydrides are well known for their novel molecular structures and useful chemical reactivity, with [B9H14]− notable in particular for its ease of isolation, unusual structure, and tautomerization. We report an experimental and theoretical investigation of the structure of [B9H14]− and the energetics of some of its reactions. Salts of [B9H14]− 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 [B9H14]− not previously observed in the solid state. Heats of formation and acid dissociation constants of [B9H14]− 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 [B9H14]− as an energy‐storage medium in ionic systems.

Effect of Boron Clusters on the Ignition Reaction of HNO3 and Dicynanamide-Based Ionic Liquids

“…A second report gives structures of B 9 H 14 − salts and suggests a new isomer exists in EIL materials. 34 The research described here includes an investigation of the experiments reported by Rogers et al on the decaborane doping of DCA − EILs. This work complements two recent studies from this research group that strive to correlate hypergolicity with the proton transfer properties of the constituent ions in an EIL.…”

Boron Hydrogen Compounds: Hydrogen Storage and Battery Applications

“…DFT calculations in the gas phase are quite reliable, and allow for obtaining good structural data and vibrational frequencies, in particular when anharmonicity is included. Several studies report the formation enthalpy of borohydride ions in the gas phase [69][70][71][72] Anharmonic DFT calculations allow for obtaining improved agreement with experimental vibrational spectra, from which heat capacity data were calculated [73]. Figure 2 compares experimental [74] and DFT calculated [69][70][71][72] formation enthalpy data for neutral and anionic boron hydrogen species.…”

“…Several studies report the formation enthalpy of borohydride ions in the gas phase [69][70][71][72] Anharmonic DFT calculations allow for obtaining improved agreement with experimental vibrational spectra, from which heat capacity data were calculated [73]. Figure 2 compares experimental [74] and DFT calculated [69][70][71][72] formation enthalpy data for neutral and anionic boron hydrogen species. Figure 2 shows that the calculated formation enthalpy for a given species (e.g., B 3 H 8 − ) can differ by about 100 kJ/mole for different sources.…”

“…Closo species, circles; nido, #; arachno, crossed squares. Data from[69][70][71][72][74][75][76]. For closo ions BnHn 2− , data (blue circles) from 2 different studies[69,72] reveal systematic differences.…”

New Reactions for Old Ions: Cage Rearrangements, Hydrolysis, and Two-Electron Reduction of nido-Decaborane in Neat 1-Ethyl-3-Methylimidazolium Acetate

“…10 We previously found that B 10 H 14 reacted spontaneously with ions from energetic azolium ILs to form stable IL-soluble species, 11 such as [B 9 H 14 ] − formed through deprotonation and rearrangement of B 10 H 14 . 12 B 10 H 14 is therefore an interesting main group probe for reactivity with [C 2 mim][OAc] because it possesses Lewis acidic sites of variable nature which may prefer the [OAc] − ion or the carbene.…”