Caesium dodecaborate is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

Cs₂B₁₂H₁₂. It is a salt composed of

caesium Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has Symbol (chemistry), symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only f ...

and dodecaborate(12) ions. The ₁₂H₁₂sup>2−

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

has been of great theoretical interest to the chemistry community.

Structure

The ₁₂H₁₂sup>2− anion's B₁₂ core is a regular

icosahedron In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes . The plural can be either "icosahedra" () or "icosahedrons". There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrical tha ...

. The ₁₂H₁₂sup>2− as a whole also has icosahedral

molecular symmetry In chemistry, molecular symmetry describes the symmetry present in molecules and the classification of these molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can be used to predict or explai ...

, and it belongs to the molecular point group I_h. Its icosahedral shape is consistent with the classification of this cage as "closo" in

polyhedral skeletal electron pair theory In chemistry the polyhedral skeletal electron pair theory (PSEPT) 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 ...

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

hydride In chemistry, a hydride is formally the anion of hydrogen (H−), a hydrogen ion with two electrons. In modern usage, this is typically only used for ionic bonds, but it is sometimes (and has been more frequently in the past) applied to all che ...

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

The dodecaborate anion was first prepared in modest yield by Pitochelli and Hawthorne from iododecarborane. It is more conventienly prepared in two steps from

sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula (sometimes written as ). It is a white crystalline solid, usually encountered as an aqueous basic solution. Sodi ...

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

boron trifluoride Boron trifluoride is the inorganic compound with the formula . This pungent, colourless, and 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 The g ...

: :4 NaBH₄ + BF₃ → NaB₃H₈ + 3 NaF + 4 H₂

Pyrolysis Pyrolysis is a process involving the Bond cleavage, separation of covalent bonds in organic matter by thermal decomposition within an Chemically inert, inert environment without oxygen. Etymology The word ''pyrolysis'' is coined from the Gree ...

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

Reactions and proposed applications

Salts of B₁₂H₁₂²⁻ have been investigated for boron neutron capture therapy and as fuels for

airbag An airbag is a vehicle occupant-restraint system using a bag designed to inflate in milliseconds during a collision and then deflate afterwards. It consists of an airbag cushion, a flexible fabric bag, an inflation module, and an impact sensor. ...

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 Carboranes (or carbaboranes) are electron-delocalized (non-classically bonded) clusters composed of boron, carbon and hydrogen atoms.Grimes, R. N., ''Carboranes 3rd Ed.'', Elsevier, Amsterdam and New York (2016), . Like many of the related boron ...

References

{{Caesium compounds Boron compounds Caesium compounds Boranes

Structure

Preparation

Reactions and proposed applications

See also

References