Caesium dodecaborate is an
inorganic compound with the
formula Cs
2B
12H
12. It is a salt composed of
caesium 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 conve ...
has been of great theoretical interest to the chemistry community.
Structure
The
12H12sup>2− anion's B
12 core is a regular
icosahedron. The
12H12sup>2− as a whole also has
icosahedral
In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes and . The plural can be either "icosahedra" () or "icosahedrons".
There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrica ...
molecular symmetry, and it belongs to the
molecular point group
Molecular symmetry in chemistry 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 explain m ...
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 Cs
2B
12H
12 feature Cs
+ ions in contact with twelve
hydride
In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride ...
s provided by four B
12H
122−. 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 Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds applica ...
. First the borohydride is converted into a triborate anion using the etherate of
boron trifluoride:
:4 NaBH
4 + BF
3 → NaB
3H
8 + 3 NaF + 4 H
2
Pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
of the triborate gives the twelve boron cluster as the sodium salt, which is then treated with caesium hydroxide to precipitate Cs
2B
12H
12.
Reactions and proposed applications
Salts of B
12H
122− have been investigated for
boron neutron capture therapy and as fuels for
airbags.
Salts of B
12H
122− are precursors to related derivatives including B
12(OH)
122− and B
12(CH
3)
122−. This closo boron hydride resists degradation more so than the isoelectronic
carboranes.
See also
*
Neutron capture therapy of cancer
References
{{reflist
Boron compounds
Caesium compounds
Boranes