Ammonia borane
4329882
217299038
2008-06-05T13:03:16Z
220.227.207.32
{{Chembox new
| Name = Ammonia borane
| ImageFile = Ammonia-borane-3D-balls.png
<!-- | ImageSize = 200px -->
| ImageName =
| IUPACName = Ammonia borane
| OtherNames = Borazane
| Section1 = {{Chembox Identifiers
| SMILES = [NH3+][BH3-]
| CASNo = 13774-81-7
| RTECS = none
}}
| Section2 = {{Chembox Properties
| Formula = H<sub>6</sub>NB
| MolarMass = 30.86534 g/mol
| Appearance = colorless, waxy solid
| Density = 0.780 g/cm<sup>3</sup><!--from Crabtree et al's x-ray study-->
| Solubility = good
| Solvent = other solvents
| SolubleOther = [[Methanol|MeOH]], [[Diethyl ether|Et<sub>2</sub>O]]
| MeltingPt = 104°C
| BoilingPt = decomposes
| pKb =
}}
| Section3 = {{Chembox Structure
| Coordination = ethane-like
| CrystalStruct = I4mm (tetragonal, >200K)
| Dipole = 5.2 [[Debye|D]]
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| MainHazards = flammable
| FlashPt =
| RPhrases = 5
| SPhrases = 14-15-26-36/37/39
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Sodium borohydride|NaBH<sub>4</sub>]],<br />[[borazine|B<sub>3</sub>N<sub>3</sub>H<sub>6</sub>]],<br />[[borane|BH<sub>3</sub>]], [[ethane|C<sub>2</sub>H<sub>6</sub>]]
}}
}}
'''Ammonia borane''' (or borazane) is the [[chemical compound]] with the formula H<sub>3</sub>NBH<sub>3</sub>. The species is the most fundamental molecular [[boron]]-[[nitrogen]] compound and has attracted recent attention as a stable storage medium for [[hydrogen]].
==Synthesis==
Reaction of [[diborane]] with [[ammonia]] mainly gives the diammoniate salt [H<sub>2</sub>B(NH<sub>3</sub>)<sub>2</sub>]<sup>+</sup>, [[borohydride|(BH<sub>4</sub>)<sup>−</sup>]]. Ammonia borane is the main product when an adduct of borane is employed in place of diborane:<ref name='shore'>{{cite journal | last = Shore | first = S.G. |coauthors = Boeddeker, K.W. | title = Large Scale Synthesis of H<sub>2</sub>B(NH<sub>3</sub>)<sub>2</sub><sup>+</sup>BH<sub>4</sub><sup>−</sup> and H<sub>3</sub>NBH<sub>3</sub> | journal = Inorganic Chemistry | year = 1964 | volume = 3 | pages = pp. 914–15 | doi = 10.1021/ic50016a038}}</ref>
:BH<sub>3</sub>([[THF]]) + NH<sub>3</sub> → BH<sub>3</sub>NH<sub>3</sub> + 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 N''H'' and the B''H'' centers.<ref name='klooster'>{{citation | last = Klooster | first = W.T. | coauthors = Koetzle, T. F.; Siegbahn, P. E. M.; Richardson, T. B.; Crabtree, R. H. | title = Study of the N-H...H-B Dihydrogen Bond Including the Crystal Structure of BH<sub>3</sub>NH<sub>3</sub> by Neutron Diffraction | journal = [[Journal of the American Chemical Society]] | year = 1999 | volume = 121 | pages = pp. 6337–6343 | doi =10.1021/ja9825332}}</ref><ref name='boese'>{{citation | last = Boese | first = R | coauthors = Niederprüm, N.; Bläser, D. | title = Molecules in Natural Science and Medicine | editor = Maksic, Z.B., Eckert-Masic, M. | Publisher = E. Horwood | location = Chichester, England | year = 1992}}</ref> 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 (NH<sub>2</sub>BH<sub>2</sub>)<sub>n</sub>, and then to (NHBH)<sub>n</sub>.<ref>"[http://www.rsc.org/chemistryworld/Issues/2006/March/HydrogenOnBoard.asp Hydrogen gets on board]", Maciej Gutowski and Tom Autrey, Royal Society of Chemistry</ref>
Borane-ammonia finds some use in [[organic synthesis]] as an air-stable derivative of diborane.<ref name='andrews'>{{citation | last = Andrews | first = G.C. | contribution = Borane–Ammonia | title = Encyclopedia of Reagents for Organic Synthesis | editor-first = L. | editor-last = Paquette | year = 2004 | publisher = [[John Wiley & Sons]] | location = [[New York]] | doi = 10.1002/047084289}}</ref>
==References==
{{reflist}}
[[Category:Inorganic compounds]]
[[Category:Boron compounds]]
[[Category:Amines]]
[[ar:بوران أمونيا]]
[[pl:Borazan]]
[[zh:硼烷氨]]