Boron hydride
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| Names | |
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IUPAC name
Diborane(6)
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| Other names
Boroethane
Boron hydride Diboron hexahydride |
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| Identifiers | |
19287-45-7 
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| 3D model (Jmol) | Interactive image |
| ChEBI |
CHEBI:33590
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| ChemSpider |
17215804
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| ECHA InfoCard | 100.039.021 |
| EC Number | 242-940-6 |
| RTECS number | HQ9275000 |
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| Properties | |
| B2H6 | |
| Molar mass | 27.67 g·mol−1 |
| Appearance | Colorless gas |
| Odor | repulsive and sweet |
| Density | 1.216 g/L |
| Melting point | −164.85 °C (−264.73 °F; 108.30 K) |
| Boiling point | −92.5 °C (−134.5 °F; 180.7 K) |
| Reacts | |
| Vapor pressure | 39.5 atm (16.6°C) |
| Structure | |
| Tetrahedral (for boron) | |
| see text | |
| 0 D | |
| Hazards | |
| Main hazards | highly flammable, reacts with water |
| Safety data sheet | See: data page |
| NFPA 704 | |
| 38 °C (100 °F; 311 K) | |
| Explosive limits | 0.8%-88% |
| Lethal dose or concentration (LD, LC): | |
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LC50 (median concentration)
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40 ppm (rat, 4 hr) 29 ppm (mouse, 4 hr) 40-80 ppm (rat, 4 hr) 159-181 ppm (rat, 15 min) |
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LCLo (lowest published)
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125 ppm (dog, 2 hr) 50 ppm (hamster, 8 hr) |
| US health exposure limits (NIOSH): | |
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PEL (Permissible)
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TWA 0.1 ppm (0.1 mg/m3) |
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REL (Recommended)
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TWA 0.1 ppm (0.1 mg/m3) |
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IDLH (Immediate danger)
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15 ppm |
| Related compounds | |
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Related boron compounds
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Decaborane BF3 |
| Supplementary data page | |
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Refractive index (n), Dielectric constant (εr), etc. |
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Thermodynamic
data |
Phase behaviour solid–liquid–gas |
| UV, IR, NMR, MS | |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is  ?) |
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| Infobox references | |
Diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless and highly unstable gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature. Synonyms include boroethane, boron hydride, and diboron hexahydride.
Diborane is a key boron compound with a variety of applications. The compound is classified as "endothermic", meaning that its heat of formation, ΔH°f is positive (36 kJ/mol). Despite a high thermodynamic instability, diborane is surprisingly nonreactive for kinetic reasons, and it is known to take part in an extensive range of chemical transformations, many of them entailing loss of dihydrogen.
Diborane adopts a D2h structure containing four terminal and two bridging hydrogen atoms. The model determined by molecular orbital theory indicates that the bonds between boron and the terminal hydrogen atoms are conventional 2-center, 2-electron covalent bonds. The bonding between the boron atoms and the bridging hydrogen atoms is, however, different from that in molecules such as hydrocarbons. Having used two electrons in bonding to the terminal hydrogen atoms, each boron has one valence electron remaining for additional bonding. The bridging hydrogen atoms provide one electron each. Thus the B2H2 ring is held together by four electrons, an example of 3-center 2-electron bonding. This type of bond is sometimes called a 'banana bond'. The lengths of the B-Hbridge bonds and the B-Hterminal bonds are 1.33 and 1.19 Å respectively, and this difference in the lengths of these bonds reflects the difference in their strengths, the B-Hbridge bonds being relatively weaker. The weakness of the B-Hbridge vs B-Hterminal bonds is indicated by their vibrational signatures in the infrared spectrum, being ~2100 and 2500 cm−1, respectively. The structure is isoelectronic with C2H62+, which would arise from the diprotonation of the planar molecule ethene. Diborane is one of many compounds with such unusual bonding.
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