Caesium dodecaborate is an inorganic compound

Inorganic compound

Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the formula

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 Cs₂B₁₂H₁₂. It is a salt, with caesium

Caesium

Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...

 cations and [B₁₂H₁₂]²⁻ anions.

Structure

The [B₁₂H₁₂]²⁻ anion's B₁₂ core is a regular icosahedron

Icosahedron

In geometry, an icosahedron is a regular polyhedron with 20 identical equilateral triangular faces, 30 edges and 12 vertices. It is one of the five Platonic solids....

. The [B₁₂H₁₂]²⁻ as a whole also has icosahedral molecular symmetry

Molecular symmetry

Molecular symmetry in chemistry describes the symmetry present in molecules and the classification of molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can predict or explain many of a molecule's chemical properties, such as its dipole moment...

, and it belongs to the molecular point group

Point groups in three dimensions

In geometry, a point group in three dimensions is an isometry group in three dimensions that leaves the origin fixed, or correspondingly, an isometry group of a sphere. It is a subgroup of the orthogonal group O, the group of all isometries that leave the origin fixed, or correspondingly, the group...

 I_h. Its icosahedral shape is consistent with the classification of this cage as "closo" in polyhedral skeletal electron pair theory

Polyhedral skeletal electron pair theory

In chemistry the polyhedral skeletal electron pair theory provides electron counting rules useful for predicting the structures of clusters such as borane and carborane clusters. The electron counting rules were originally formulated by Kenneth Wade and were further developed by D. M. P. Mingos and...

.

Crystals of Cs₂B₁₂H₁₂ feature Cs⁺ ions in contact with twelve hydride

Hydride

In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...

s provided by four B₁₂H₁₂²⁻. The B-B bond distances are 178 pm, and the B-H distances are 112 pm. Many other salts are known.

Preparation

It is prepared in two steps from sodium borohydride

Sodium borohydride

Sodium borohydride, also known as sodium tetrahydridoborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as a powder, is a versatile reducing agent that finds wide application in chemistry, both in the laboratory and on a technical scale. Large amounts are...

. First the borohydride is converted into a triborate anion using the etherate of boron trifluoride

Boron trifluoride

Boron trifluoride is the chemical compound with the formula BF3. This pungent colourless toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.-Structure and bonding:...

:

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 boron neutron capture therapy

Boron Neutron Capture Therapy

Boron neutron capture therapy is an experimental form of radiotherapy that uses a neutron beam that interacts with boron injected into a patient...

 and as fuels for airbag

Airbag

An Airbag is a vehicle safety device. It is an occupant restraint consisting of a flexible envelope designed to inflate rapidly during an automobile collision, to prevent occupants from striking interior objects such as the steering wheel or a window...

s.

Salts of B₁₂H₁₂²⁻ are precursors to related derivatives including B₁₂(OH)₁₂²⁻ and B₁₂(CH₃)₁₂²⁻. This closo boron hydride resists degradation more so than the isoelectronic carborane

Carborane

A carborane is a cluster composed of boron and carbon atoms. Like many of the related boranes, these clusters are polyhedra and are similarly classified as closo-, nido-, arachno-, hypho-, etc...

s.