tetraborane

The class of boranes was elucidated using X-ray diffraction analysis by Lipscomb et al. in the 1950s. The X-ray data indicated two-electron multicenter bonds. Later, analysis based on high-resolution X-ray data was performed to analyze the charge density.{{Cite journal|last1=Förster|first1=Diana|last2=Hübschle|first2=Christian B.|last3=Luger|first3=Peter|last4=Hügle|first4=Thomas|last5=Lentz|first5=Dieter|date=2008|title=On the 2-Electron 3-Center B−H−B Bond: Charge Density Determination of Tetraborane(10)|url=https://pubs.acs.org/doi/10.1021/ic701924r|journal=Inorganic Chemistry|language=en|volume=47|issue=6|pages=1874–1876|doi=10.1021/ic701924r|pmid=18271535|issn=0020-1669}}

Like other boron hydride clusters, the structure of tetraborane involves multicenter bonding, with hydrogen bridges or protonated double bonds. According to its formula, B₄H₁₀, it is classified as an arachno-cluster and has a butterfly geometry, which can be rationalized by Wade's rules.Grimes, Russel N. "Boron." Advanced Inorganic Chemistry. By F. Albert Cotton, Geoffrey Wilkinson, Carlos A. Murillo, and Manfred Bochmann. 6th ed. N.p.: n.p., 1999. 143-46. Print. Each boron is sp³ hybridized, and “the configuration of the three hydrogens surrounding borons B1 and B3 is approximately trigonal and suggests approximately tetrahedral hybridization for these borons which would predict bond angles of 120°.”Lipscomb, William N. Boron Hydrides. New York: W. A. Benjamin, 1963. Print.{{Rp|35}} However, the boron arrangements can be classified as fragments of either the icosahedron or the octahedron because the bond angles are actually between 105° and 90°.{{Rp|3}}

The comparison of the diffraction data from X-ray diffraction and electron diffraction gave suspected bond lengths and angles: B1—B2 = 1.84 Å, B1—B3= 1.71 Å, B2—B1—B4= 98 ̊, B—H = 1.19 Å, B1—Hμ = 1.33 Å, B2—Hμ =1.43 Å.{{Rp|3}}

Tetraborane can be produced via a reaction between acid and magnesium or beryllium borides, with smaller quantities from aluminum, manganese, and cerium borides.{{Cite book |last=Stock |first=Alfred |url=https://archive.org/details/hydridesofborons0000alfr/ |title=Hydrides of Boron and Silicon |publisher=Cornell University Press |year=1933 |pages=60}} Hydrolysis of magnesium boride, hydrogenation of boron halides at high temperatures and the pyrolysis of diborane also produce tetraborane. The hydrolysis of magnesium boride was one of the first reactions to give a workable yield (14%) of tetraborane.{{Citation needed|date=July 2023}} Phosphoric acid proved to be the most efficient acid (compared to hydrochloric and sulfuric acid) in the reaction with magnesium boride.{{sfn|Stock|1933|p=41}}

Alternatively, boron trihalides metathesize with arachno-triborate(8) (B₃H{{su|b=8|p=−}}) salts to give tetraborane and a hydridotrihaloborate salt with yields near 50%.{{cite journal|doi=10.1021/ic00135a048|pp=1952-1957|journal=Inorganic Chemistry|volume=1982|issue=21|title=New, systematic syntheses of boron hydrides via hydride ion abstraction reactions: Preparation of B₂H₆, B₄H₁₀, B₅H₁₁, and B₁₀H₁₄|first1=Mark A.|last1=Toft|first2=J. B.|last2=Leach|first3=Francis L.|last3=Himpsl|first4=Sheldon G.|last4=Shore|orig-date=20 Oct 1981|publisher=American Chemical Society}}

Scientists are currently{{When|date=August 2020}} working to produce the bis(diboranyl) isomer of the arachno-tetraborane structure. The bis(diboranyl) is expected to have a lower energy at the Hartree-Fock method (HF) level. There is some evidence that the bis(diboranyl) isomer is initially produced when synthesizing tetraborane by the Wurtz reaction or coupling of B₂H₅I in the presence of sodium amalgam. Three pathways of conversion from the bis(diboranyl) isomer into the arachno-tetraborane structure have been constructed computationally.

:Path 1: Dissociative pathway via B₃H₇ and BH₃

:Path 2: Concerted pathway over two transition states separated by a local minimum

:Path 3: Another concerted pathway involving penta-coordinated isomers as intermediates

Paths 2 and 3 are more likely, because they are more energetically favored with energies of 33.1 kcal/mol and 22.7 kcal/mol respectively.{{Cite journal|last1=Ramakrishna|first1=Vinutha|last2=Duke|first2=Brian J.|date=2004|title=Can the Bis(diboranyl) Structure of B4H10 Be Observed? The Story Continues|url=https://pubs.acs.org/doi/10.1021/ic049558o|journal=Inorganic Chemistry|language=en|volume=43|issue=25|pages=8176–8184|doi=10.1021/ic049558o|pmid=15578859|issn=0020-1669}}

Because it is easily oxidized it must be kept under vacuum. Tetraborane ignites when it comes in contact with air, oxygen, and nitric acid. Boranes in general including tetraborane have been deemed very toxic and are biologically destructive. A study consisting of small daily exposure of the chemical to rabbits and rats resulted in fatality.{{cite web |url=http://voh.chem.ucla.edu/vohtar/spring05/classes/172/pdf/p21-30Borane.pdf |title=Archived copy |access-date=2011-05-11 |url-status=dead |archive-url=https://web.archive.org/web/20110727012047/http://voh.chem.ucla.edu/vohtar/spring05/classes/172/pdf/p21-30Borane.pdf |archive-date=2011-07-27 }}

{{Reflist}}

• {{cite web|url=http://www.webelements.com/compounds/boron/tetraborane_10.html |title=Boron»tetraborane (10) [WebElements Periodic Table] |website=Webelements.com |access-date=2017-06-07}}
• {{cite web |url=http://osulibrary.orst.edu/specialcollections/rnb/23/23-184.html |title=Linus Pauling Research Notebooks - Special Collections & Archives Research Center |website=Osulibrary.orst.edu |access-date=2017-06-07 |archive-date=2012-07-17 |archive-url=https://web.archive.org/web/20120717062712/http://osulibrary.orst.edu/specialcollections/rnb/23/23-184.html |url-status=dead }}

{{Boron compounds}}

{{Hydrides by group}}

Category:Boranes

Category:Foul-smelling chemicals