Caesium dodecaborate

Caesium dodecarborate is an inorganic compound with the formula Cs₂B₁₂H₁₂. It is a salt, with caesium cations and [B₁₂H₁₂]^2- anions.

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Structure

The anion has a icosahedral shape, belonging to the point group symmetry I_h. Its icosahedral shape is consistent with the classification of this cage as "closo."

Crystals of Cs₂B₁₂H₁₂ feature Cs⁺ ions in contact with twelve hydrides provided by four B₁₂H₁₂^2-. The B-B bond distances are 178 pm, and the B-H distances are 112 pm.^[1] Many other salts are known.^[2]

Preparation

It is prepared in two steps from sodium borohydride. First the borohydride is converted into a triborate anion using the etherate of boron trifluoride:

4 NaBH₄ + BF₃ → NaB₃H₈ + 3 NaF + 4 H₂

Pyrolysis of the triborate gives the twelve boron cluster as the sodium salt, which is then treated with caesium hydroxide to precipitate Cs₂B₁₂H₁₂.

Applications

Salts of B₁₂H₁₂^2- have been investigated for neutron-capture therapy and as fuels for airbags.^[3]

Salts of B₁₂H₁₂^2- are precursors to related derivatives including B₁₂(OH)₁₂^2- and B₁₂(CH₃)₁₂^2-. This closo boron hydride resists degradation moreso than the isoelectronic carboranes.

References

1. ^ Ioannis Tiritiris, Thomas Schleid, Klaus Müller, Wilhelm Preetz “Strukturelle Untersuchungen an Cs₂[B₁₂H₁₂]” Zeitschrift für anorganische und allgemeine Chemie 2000, Volume 626, Issue 2, pp. 323-325.
2. ^ Ioannis Tiritiris, Nguyen-Duc Van, Thomas Schleid “Synthesis and Crystal Structure of [Ni(H₂O)₆][B₁₂H₁₂]·6 H₂O” Zeitschrift für anorganische und allgemeine Chemie 2004, Volume 630, Issue 11 pp 1763. DOI: 10.1002/zaac.200470138.
3. ^ Igor B. Sivaev, Vladimir I. Bregadze, and Stefan Sjoberg “Chemistry of closo-Dodecaborate Anion [B₁₂H₁₂]^2-: A Review” Collection of Czechoslovak Chemical Communications 2002, 67(6), 679-727. doi:10.1135/cccc20020679.