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Ammonia borane



Ammonia borane
IUPAC name Ammonia borane
Identifiers
CAS number 13774-81-7
RTECS number none
SMILES [NH3+][BH3-]
Properties
Molecular formula H6NB
Molar mass 30.86534 g/mol
Appearance colorless, waxy solid
Density 0.780 g/cm3
Melting point

104 C °C

Boiling point

decomposes

Solubility in water good
Solubility in other solvents MeOH, Et2O
Structure
Crystal structure I4mm (tetragonal, >200K)
Coordination
geometry
ethane-like
Dipole moment 5.2 D
Hazards
Main hazards flammable
R-phrases 5
S-phrases 14-15-26-36/37/39
Related Compounds
Related compounds NaBH4,
B3N3H6,
BH3, C2H6
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Ammonia borane is the chemical compound with the formula H3NBH3. The species is the most fundamental molecular boron-nitrogen compound and has attracted recent attention as a stable storage medium for hydrogen.

Additional recommended knowledge

Contents

Synthesis

Reaction of diborane with ammonia mainly gives the diammoniate salt [H2B(NH3)2]+, (BH4). Ammonia borane is the main product when an adduct of borane is employed in place of diborane:[1]

BH3(THF) + NH3 → BH3NH3 + THF

Properties and structure

It can be described as an hydride of nitrogen and boron, but its behavior indicates that the H atoms attached to boron are hydridic and those attached to nitrogen are somewhat acidic. It is a solid, formally isoelectronic with ethane. Obviously its similarity to ethane is tenuous since borane-ammonia is a solid and ethane is a gas (m.p. −181 °C), their melting points differing by 284 °C. Understanding this difference has been the subject of an ongoing discussion for many years.

The B-N distance is 1.58(2) Å. The B-H and N-H distances are 1.15 and 0.96 Å, respectively.

The structure of the solid indicates a close association of the NH and the BH centers.[2] The original crystallographic analysis of this compound reversed the assignments of B and N. The updated structure was arrived at with improved data using the technique of neutron diffraction that allowed the hydrogen atoms to be located with greater precision.

Uses

Ammonia borane has been suggested as a source of hydrogen for use in motor vehicles as it can be made to release hydrogen on heating, being polymerized first to (NH2BH2)n, and then to (NHBH)n.[3]

Borane-ammonia finds some use in organic synthesis as an air-stable derivative of diborane.[4]

References

  1. ^ Shore, S. G.; Boeddeker, K. W. “Large Scale Synthesis of H2B(NH3)2+BH4 and H3NBH3. Inorganic Chemistry 1964, volume 3, pages 914-15. DOI: 10.1021/ic50016a038
  2. ^ Klooster, W. T.; Koetzle, T. F.; Siegbahn, P. E. M.; Richardson, T. B.; Crabtree, R. H., "Study of the N-H...H-B Dihydrogen Bond Including the Crystal Structure of BH3NH3 by Neutron Diffraction", Journal of the American Chemical Society, 1999, volume 121, pages 6337-6343. DOI: 10.1021/ja9825332. Boese, R.; Niederprüm, N.; Bläser, D. In "Molecules in Natural Science and Medicine; Maksic, Z. B., Eckert-Masic, M., Eds.; E. Horwood: Chichester, England, 1992.
  3. ^ "Hydrogen gets on board", Maciej Gutowski and Tom Autrey, Royal Society of Chemistry
  4. ^ Andrews, G. C. "Borane–Ammonia" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ammonia_borane". A list of authors is available in Wikipedia.
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