Ammonia borane
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| Ammonia borane | |
|---|---|
| Image:Ammonia-borane-3D-balls.png | |
| General | |
| Systematic name | Ammonia borane |
| Other names | ? |
| Molecular formula | H6NB |
| SMILES | ? |
| Molar mass | 30.86 g/mol |
| Appearance | colorless, waxy solid |
| CAS number | [[13774-81-7] |
| Properties | |
| Density and phase | 0.780 g/cm3 |
| Solubility in water | good |
| Other solvents | MeOH, Et2O |
| Melting point | 104 C °C |
| Boiling point | decomposes |
| Basicity (pKb) | ? |
| Structure | |
| Coordination geometry | ethane-like |
| Crystal structure | I4mm (tetragonal, >200K) |
| Dipole moment | 5.2 D |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | flammable |
| NFPA 704 | |
| Flash point | ? °C |
| R/S statement | R: 5 S: 14-15-26-36/37/39 |
| RTECS number | none |
| Supplementary data page | |
| Structure and properties | n, εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| 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.
Contents |
[edit] 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:<ref>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</ref>
- BH3(THF) + NH3 → BH3NH3 + THF
[edit] 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.<ref>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.</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.
[edit] 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.
Borane-ammonia finds some use in organic synthesis as an air-stable derivative of diborane.<ref>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.</ref>
[edit] References
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