Boron monohydride

Borane(1), boron monohydride, hydridoboron or borylene is an unstable molecule of boron and hydrogen with formula BH.

Boron monohydride
Names
IUPAC name
λ1-borane
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
33
Properties
BH
Molar mass 11.82 g·mol−1
Thermochemistry[1]
172
442.7
412.7
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Formation

Boron monohydride can be formed from borane carbonyl exposed to ultraviolet light. BH3CO → BH + CH2O[2]

Boron monohydride is formed when boron compounds are heated to a high temperature in the presence of hydrogen.[3]

Boron monohydride is formed when the boron anion B− reacts with a hydrogen ion H+. It is also formed when atomic boron reacts with hydrogen. B + H2 → BH + H. There is too much energy in the reaction for BH2 to be stable.[4]

Boron monohydride probably exists in sunspots,[5] but as of 2008 has not been detected.[6]

Properties

The ionization potential is around 9.77 eV.[7] The dissociation energy for the ground state molecule is 81.5 kcal/mol.[8] The electron affinity is roughly 0.3 eV, and the HB− ion is formed.[9]

The dipole moment of the molecule in its ground state is 1.27 debye and for the first excited electronic state A1Π is 0.58 debye.[10]

The spectrum of boron monohydride includes a molecular band for the lowest electronic transition X1Σ+ → A1Π with a band head at 433.1 nm (for 0→0) and 437.1 (for 0→1)[3] The spectrum contains P, Q, and R branches.[10]

Although BH is a closed shell molecule, it is paramagnetic independent of temperature.[11]

Reactions

Boron monohydride is unstable in bulk and disappears quickly on a timescale of 20 ns when at a pressure of 20 Torr.[12] Boron monohydride reacts with oxygen, probably forming HBO.[2] Boron monohydride shows no reaction with methane, but reacts with propane to give C3H7BH2. With nitric oxide (NO) it probably yields HBO and HBNO. Boron monohydride appears to add onto double bonds in unsaturated organic compounds. It also reacts with water.[2]

Boron monohydride can take on the form of solid poly-borane(1) which spontaneously inflames in air.[13]

Solid BH is predicted to take on an Ibam phase at pressures over 50 GPa and then become a metallic P6/mmm phase over 168 GPa.[14]

Ions

Both a cation and a dication are known. The dication HB2+ can be supported by a σ-donating ligand framework with two links.[15] The dianion can also be stabilized by an amine.[16]

References
  1. "GROMACS Molecule Database - boron-monohydride". virtualchemistry.org.
  2. Garland, Nancy L.; Stanton, C. T.; Fleming, James W.; Baronavski, A. P.; Nelson, H. H. (June 1990). "Boron monohydride reaction kinetics studied with a high-temperature reactor". The Journal of Physical Chemistry. 94 (12): 4952–4956. doi:10.1021/j100375a036.
  3. Abad, Carlos; Florek, Stefan; Becker-Ross, Helmut; Huang, Mao-Dong; Heinrich, Hans-Joachim; Recknagel, Sebastian; Vogl, Jochen; Jakubowski, Norbert; Panne, Ulrich (October 2017). "Determination of boron isotope ratios by high-resolution continuum source molecular absorption spectrometry using graphite furnace vaporizers". Spectrochimica Acta Part B: Atomic Spectroscopy. 136: 116–122. Bibcode:2017AcSpe.136..116A. doi:10.1016/j.sab.2017.08.012.
  4. Yang, Xuefeng; Dagdigian, Paul J. (1993). "Chemiluminescence spectra and cross sections for the reaction of boron(4p 2P) with hydrogen and deuterium". The Journal of Physical Chemistry. 97 (17): 4270–4276. doi:10.1021/j100119a006. ISSN 0022-3654.
  5. Engvold, O. (February 1970). "The diatomic molecules BH, BN, and BO in sunspots and the solar abundance of boron". Solar Physics. 11 (2): 183–197. Bibcode:1970SoPh...11..183E. doi:10.1007/BF00155219. S2CID 119720128.
  6. Karthikeyan, B; Bagare, S; Rajamanickam, N; Raja, V (February 2009). "On the search for BF, BH and BS molecular lines in sunspot spectra". Astroparticle Physics. 31 (1): 6–12. Bibcode:2009APh....31....6K. doi:10.1016/j.astropartphys.2008.10.009.
  7. Haynes, William M. (2012). CRC Handbook of Chemistry and Physics, 93rd Edition. CRC Press. p. 10–200. ISBN 9781439880494.
  8. Bauschlicher, Charles W.; Langhoff, Stephen R.; Taylor, Peter R. (July 1990). "On the dissociation energy of BH". The Journal of Chemical Physics. 93 (1): 502–506. Bibcode:1990JChPh..93..502B. doi:10.1063/1.459550.
  9. Reid, C.J. (August 1993). "Electron affinities of BH, B2, BC and BN molecules determined using charge inversion spectrometry". International Journal of Mass Spectrometry and Ion Processes. 127: 147–160. Bibcode:1993IJMSI.127..147R. doi:10.1016/0168-1176(93)87087-9.
  10. Thomson, Ritchie; Dalby, F. W. (June 1969). "An experimental determination of the dipole moments of the X ( 1 Σ) and A ( 1 Π) states of the BH molecule". Canadian Journal of Physics. 47 (11): 1155–1158. Bibcode:1969CaJPh..47.1155T. doi:10.1139/p69-144.
  11. Fowler, P.W.; Steiner, E. (20 December 1991). "Paramagnetic closed-shell molecules: the isoelectronic series CH + , BH and BeH -". Molecular Physics. 74 (6): 1147–1158. Bibcode:1991MolPh..74.1147F. doi:10.1080/00268979100102871.
  12. Bauer, S. H. (January 1996). "Oxidation of B, BH, BH3, and BmHn Species: Thermochemistry and Kinetics". Chemical Reviews. 96 (6): 1907–1916. doi:10.1021/cr941034q. PMID 11848815.
  13. Urben, Peter (2013). Bretherick's Handbook of Reactive Chemical Hazards. Elsevier. p. 71. ISBN 9780080523408.
  14. Hu, Chao-Hao; Oganov, Artem R.; Zhu, Qiang; Qian, Guang-Rui; Frapper, Gilles; Lyakhov, Andriy O.; Zhou, Huai-Ying (19 April 2013). "Pressure-Induced Stabilization and Insulator-Superconductor Transition of BH". Physical Review Letters. 110 (16): 165504. Bibcode:2013PhRvL.110p5504H. doi:10.1103/PhysRevLett.110.165504. PMID 23679618.
  15. Chen, Wen-Ching; Lee, Ching-Yu; Lin, Bo-Chao; Hsu, Yu-Chen; Shen, Jiun-Shian; Hsu, Chao-Ping; Yap, Glenn P. A.; Ong, Tiow-Gan (10 January 2014). "The Elusive Three-Coordinate Dicationic Hydrido Boron Complex". Journal of the American Chemical Society. 136 (3): 914–917. doi:10.1021/ja4120852. PMID 24383448.
  16. Vargas-Baca, Ignacio; Findlater, Michael; Powell, Adam; Vasudevan, Kalyan V.; Cowley, Alan H. (2008). "Boron di- and tri-cations". Dalton Transactions (45): 6421–6. doi:10.1039/b810575h. PMID 19002329.
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