Editing Boron (section)

==Chemical compounds==
{{Main|boron compounds}}

===General trends===
In some ways, boron is comparable to [[carbon]] in its capability to form stable [[covalent bond|covalently bonded]] molecular networks (even nominally disordered ([[Amorphous solid|amorphous]]) boron contains boron [[icosahedra]], which are bonded randomly to each other without [[long-range order]].<ref>{{Cite journal| title=A neutron diffraction study of amorphous boron|author = Delaplane, R.G.|journal = Journal of Non-Crystalline Solids| volume=104| date=1988| pages=249–252| doi=10.1016/0022-3093(88)90395-X| last2=Dahlborg| first2=U.| last3=Graneli| first3=B.| last4=Fischer| first4=P.| last5=Lundstrom| first5=T.| issue=2–3| bibcode=1988JNCS..104..249D}}</ref><ref>{{Cite journal| title = A neutron diffraction study of amorphous boron using a pulsed source| author=R.G. Delaplane| journal=Journal of Non-Crystalline Solids| volume=106| issue=1–3| date=1988| pages=66–69| doi = 10.1016/0022-3093(88)90229-3| last2=Dahlborg| first2=U.| last3=Howells| first3=W.| last4=Lundstrom| first4=T.| bibcode = 1988JNCS..106...66D}}</ref>).  In terms of chemical behavior, boron compounds [[diagonal relationship|resembles]] [[silicon]]. [[Aluminium]], the heavier congener of boron, does not behave analogously to boron: it is far more electropositive, it is larger, and it tends not to form homoatomic Al-Al bonds. In the most familiar compounds, boron has the formal oxidation state III. These include the common oxides, sulfides, nitrides, and halides, as well as organic derivatives<ref name="HollemanAF" />

Boron compounds often violate the [[octet rule]].<ref name="Key">{{Cite web |url=https://opentextbc.ca/introductorychemistry/chapter/violations-of-the-octet-rule-2/ |title=Violations of the Octet Rule |last=Key |first=Jessie A. |date=14 September 2014 |website=Introductory Chemistry |access-date=14 August 2019 |archive-date=17 May 2019 |archive-url=https://web.archive.org/web/20190517090709/https://opentextbc.ca/introductorychemistry/chapter/violations-of-the-octet-rule-2/ |url-status=live }}</ref><ref name="ReferenceA"/>

===Halides===
Boron forms the complete series of trihalides, i.e. BX<sub>3</sub> (X = F, Cl, Br, I).  The trifluoride is produced by treating borate salts with [[hydrogen fluoride]], while the trichloride is produced by [[Carbothermic reaction|carbothermic]] reduction of boron oxides in the presence of chlorine gas:<ref name=Brotherton>{{cite book |doi=10.1002/14356007.a04_309 |chapter=Boron Compounds |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2000 |last1=Brotherton |first1=Robert J. |last2=Weber |first2=C. Joseph |last3=Guibert |first3=Clarence R. |last4=Little |first4=John L. |isbn=978-3-527-30385-4 }}</ref><ref name="HollemanAF" />
:{{chem2|B2O3  + 3 C  + 6 Cl2  ->  2 BCl3  +  3 CO}}

[[File:Boron-trifluoride-pi-bonding-2D.png|class=skin-invert-image|upright|thumb|left|[[Boron trifluoride|Boron (III) trifluoride]] structure, showing "empty" boron p orbital in pi-type [[coordinate covalent bond]]s]]

The trihalides adopt a planar trigonal structures, in contrast to the behavior of aluminium trihalides. All charge-neutral boron halides violate the octet rule, hence they typically are [[Lewis acid]]ic. For example, [[boron trifluoride]] (BF<sub>3</sub>) combines eagerly with fluoride sources to give the [[tetrafluoroborate]] anion, BF<sub>4</sub><sup>−</sup>. Boron trifluoride is used in the petrochemical industry as a catalyst. The halides react with water to form [[boric acid]].<ref name="HollemanAF" />  Other boron halides include those with B-B bonding, such as [[Diboron tetrafluoride|B<sub>2</sub>F<sub>4</sub>]] and B<sub>4</sub>Cl<sub>4</sub>.<ref name=Greenwood&Earnshaw2nd/>

===Oxide derivatives===
Boron-containing minerals exclusively exist as oxides of B(III), often associated with other elements. More than one hundred [[borate mineral]]s are known. These minerals resemble silicates in some respect, although it is often found not only in a tetrahedral coordination with oxygen, but also in a trigonal planar configuration. The borates can be subdivided into two classes, anhydrous and the far more common hydrates.  The hydrates contain B-OH groups and sometimes water of crystallization. A typical motif is exemplified by the tetraborate anions of the common mineral [[borax]]. The formal negative charge of the tetrahedral borate center is balanced by sodium (Na<sup>+</sup>).<ref name="HollemanAF" /> Some idea of the complexity of these materials is provided by the inventory of zinc borates, which are common [[wood preservative]]s and [[fire retardant]]s:<ref name=UllBO>{{cite book |doi=10.1002/14356007.a04_263.pub2 |chapter=Boric Oxide, Boric Acid, and Borates |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2015 |last1=Schubert |first1=David M. |pages=1–32 |isbn=978-3-527-30385-4 }}</ref> 4ZnO·B<sub>2</sub>O<sub>3</sub>·H<sub>2</sub>O, ZnO·B<sub>2</sub>O<sub>3</sub>·1.12H<sub>2</sub>O, ZnO·B<sub>2</sub>O<sub>3</sub>·2H<sub>2</sub>O, 6ZnO·5B<sub>2</sub>O<sub>3</sub>·3H<sub>2</sub>O, 2ZnO·3B<sub>2</sub>O<sub>3</sub>·7H<sub>2</sub>O, 2ZnO·3B<sub>2</sub>O<sub>3</sub>·3H<sub>2</sub>O, 3ZnO·5B<sub>2</sub>O<sub>3</sub>·14H<sub>2</sub>O, and ZnO·5B<sub>2</sub>O<sub>3</sub>·4.5H<sub>2</sub>O.<ref name=Schubert>{{cite journal |doi=10.1021/cm020791z |title=Structural Characterization and Chemistry of the Industrially Important Zinc Borate, Zn&#91;B<sub>3</sub>O<sub>4</sub>(OH)<sub>3</sub>&#93; |date=2003 |last1=Schubert |first1=David M. |last2=Alam |first2=Fazlul |last3=Visi |first3=Mandana Z. |last4=Knobler |first4=Carolyn B. |journal=Chemistry of Materials |volume=15 |issue=4 |pages=866–871 }}</ref>

As illustrated by the preceding examples, borate anions tend to condense by formation of B-O-B bonds.  Borosilicates, with B-O-Si, and borophosphates, with B-O-P linkages, are also well represented in both minerals and synthetic compounds.<ref>{{Cite web|url=https://www.mindat.org/|title=Mindat.org - Mines, Minerals and More|website=mindat.org|access-date=4 August 2019|archive-date=22 April 2011|archive-url=https://web.archive.org/web/20110422205859/http://www.mindat.org/|url-status=live}}</ref>

Related to the oxides are the [[alkoxide]]s and [[boronic acid]]s with the formula B(OR)<sub>3</sub> and R<sub>2</sub>BOH, respectively.  Boron forms a wide variety of such metal-organic compounds, some of which are used in the synthesis of pharmaceuticals. These developments, especially the [[Suzuki reaction]], was recognized with the 2010 [[Nobel Prize in Chemistry]] to [[Akira Suzuki]].<ref>{{cite web|last=Nobelprize.org|title=The Nobel Prize in Chemistry 2010|url=https://www.nobelprize.org/nobel_prizes/chemistry/laureates/2010/|publisher=Nobel Prize Foundation|access-date=2013-10-25}}</ref>

===Hydrides===
{{Main|Boranes}}
[[File:Deltahedral-borane-cluster-array-numbered-3D-bs-17.png|thumb|[[Ball-and-stick model]]s showing the structures of the boron skeletons of [[Boranes|borane]] [[Atom cluster|clusters]]. The structures can be rationalised by [[polyhedral skeletal electron pair theory]].<ref>{{cite journal|title=The significance and impact of Wade's rules |first=Alan J. |last=Welch |journal=Chem. Commun. |date=2013|volume=49 |issue=35 |pages=3615–3616 |doi=10.1039/C3CC00069A|pmid=23535980 }}</ref>]]

Boranes and [[borohydride]]s are neutral and anionic compounds of boron and hydrogen, respectively.  [[Sodium borohydride]] is the progenitor of the boranes.  Sodium borohydride is obtained by [[hydrogenation]] of [[trimethylborate]]:<ref name=Brotherton/>
:{{chem2|B(OCH3)3  +  4 Na  +  2H2 ->  NaBH4  +  3 NaOCH3}}
Sodium borohydride is a white, fairly air-stable salt.

Sodium borohydride converts to diborane by treatment with [[boron trifluoride]]:<ref name=Brotherton/>
:{{chem2|3 NaBH4  +  4 BF3 ->  2 (BH3)2  +  3 NaBF4}}
[[Diborane]] is the dimer of the elusive parent called [[borane]], BH<sub>3</sub>. Having a formula akin to ethane's (C<sub>2</sub>H<sub>6</sub>), diborane adopts a very different structure, featuring a pair of bridging H atoms.  This unusual structure, which was deduced only in the 1940s, was an early indication of the many surprises provided by boron chemistry.<ref name=Brotherton/>
[[image:Diborane-2D-dimensions.svg|class=skin-invert-image|thumb|left|220px|Structure of diborane]]

Pyrolysis of diborane gives [[boron hydride cluster]]s, such as [[pentaborane(9)]] {{chem2|B5H9}} and [[decaborane]] {{chem2|B10H14}}.<ref name=Greenwood&Earnshaw2nd>{{Greenwood&Earnshaw2nd}}</ref>{{rp|pp=164,170,173}} A large number of anionic boron hydrides are also known, e.g. [[dodecaborate|[B<sub>12</sub>H<sub>12</sub>]<sup>2−</sup>]].   In these [[cluster compound]]s, boron has a [[coordination number]] greater than four.<ref name="HollemanAF" /> The analysis of the bonding in these polyhedra clusters earned [[William N. Lipscomb]] the 1976 Nobel Prize in Chemistry for "studies on the structure of boranes illuminating problems of chemical bonding".  Not only are their structures unusual, many of the boranes are extremely reactive. For example, a widely used procedure for [[pentaborane]] states that it will "spontaneously inflame or explode in air".<ref>{{cite book |doi=10.1002/9780470132463.ch26 |chapter=Pentaborane(9) (B <sub>5</sub> H <sub>9</sub> ) |title=Inorganic Syntheses |date=1974 |last1=Miller |first1=V. R. |last2=Ryschkewitsch |first2=G. E. |last3=Gaines |first3=D. F. |last4=Keipe |first4=N. |volume=15 |pages=118–122 |isbn=978-0-470-13176-3 }}</ref>

===Organoboron compounds===
{{Main|Organoboron chemistry}}
A large number of organoboron compounds, species with B-C bonds, are known. Many organoboron compounds are produced from [[hydroboration–oxidation reaction|hydroboration]], the addition of [[boranes|B-H bonds]] to {{chem2|C\dC and C\tC}} bonds.<ref>{{March6th|page=1075}}</ref> [[Diborane]] is traditionally used for such reactions, as illustrated by the preparation of trioctylborane:<ref>{{cite journal |doi=10.15227/orgsyn.053.0077 |title=Ketones and Alcohols from Organoboranes: Phenyl Heptyl Ketone, 1-Hexanol, and 1-Octanol |journal=Organic Syntheses |date=1973 |volume=53 |page=77|first1=Hiromichi |last1=Kono|first2=John|last2=Hooz }}</ref>
:{{chem2|B2H6  +  6 H2C\dCH(CH2)5CH3 ->  2 B((CH2)7CH3)3}}
This [[regiochemistry]], i.e. the tendency of B to attach to the terminal carbon - is explained by the polarization of the bonds in boranes, which is indicated as B<sup>δ+</sup>-H<sup>δ-</sup>.<ref name="Greenwood&Earnshaw2nd"/>{{rp|pp=144, 166}}

Hydroboration opened the doors for many subsequent reactions, several of which are useful in [[organic synthesis|the synthesis of complex organic compounds]].<ref name = HCB>{{cite book|author=Herbert C. Brown|publisher=John Wiley and Sons|location=New York|year=1975|title=Organic Syntheses via Boranes|isbn=0471112801}}</ref>   The significance of these methods was recognized by the award of [[Nobel Prize in Chemistry]] to [[H. C. Brown]] in 1979. Even complicated boron hydrides, such as [[decaborane]] undergo hydroboration.<ref>{{Greenwood&Earnshaw2nd|page=181}}</ref>  Like the volatile boranes, the alkyl boranes ignite spontaneously in air.

In the 1950s, several studies examined the use of [[boranes]] as energy-increasing "[[Zip fuel]]" additives for jet fuel.<ref>{{Cite book |last=Griswold |first=Wesley |chapter-url=https://books.google.com/books?id=Sy0DAAAAMBAJ&pg=PA86 |title=Popular Science |date=October 1957 |publisher=Bonnier Corporation |pages=86–89 |language=en |chapter=Super-Potent 'Zip' Fuels Pack More WHOOSH}}</ref>

Triorganoboron(III) compounds are trigonal planar and exhibit weak [[Lewis acid]]ity.  The resulting adducts are tetrahedral. This behavior contrasts with that of tri[[organoaluminium compound]]s (see [[trimethylaluminium]]), which are tetrahedral with bridging alkyl groups.{{Citation needed|date=December 2024}}

A compound with the B≡C triple bond was synthesized for the first time in 2025.<ref>{{Cite journal |last1=Michel |first1=Maximilian |last2=Kar |first2=Sourav |last3=Endres |first3=Lukas |last4=Dewhurst |first4=Rian D. |last5=Engels |first5=Bernd |last6=Braunschweig |first6=Holger |date=2025-03-04 |title=The synthesis of a neutral boryne |url=https://www.nature.com/articles/s44160-025-00763-1 |journal=Nature Synthesis |language=en |pages=1–8 |doi=10.1038/s44160-025-00763-1 |issn=2731-0582}}</ref>

===Nitrides===
{{Main|Boron nitride}}
The boron-nitrides follow the pattern of avoiding B-B and N-N bonds: only B-N bonding is observed generally.  The [[boron nitride]]s exhibit structures analogous to various [[allotropes of carbon]], including graphite, diamond, and nanotubes.  This similarity reflects the fact that B and N have eight valence electrons as does a pair of carbon atoms.  In cubic boron nitride (tradename [[Borazon]]), boron and nitrogen atoms are tetrahedral, just like carbon in [[diamond]]. Cubic boron nitride, among other applications, is used as an abrasive, as its [[hardness]] is comparable with that of diamond. Hexagonal boron nitride (h-BN) is the BN analogue of graphite, consisting of sheets of alternating B and N atoms.  These sheets stack with boron and  nitrogen in registry between the sheets. Graphite and h-BN have very different properties, although both are lubricants, as these planes slip past each other easily. However, h-BN is a relatively poor electrical and thermal conductor in the planar directions.<ref name="dkg">{{cite journal| title = Hexagonal Boron Nitride (hBN) – Applications from Metallurgy to Cosmetics| url = http://www.esk.com/uploads/tx_userjspresseveroeff/PR_0712_CFI_12-2007_Hexagonales-BN_e_01.pdf| author = Engler, M.| journal = Cfi/Ber. DKG| volume = 84| date = 2007| page = D25| issn = 0173-9913| access-date = 8 January 2012| archive-date = 13 June 2013| archive-url = https://web.archive.org/web/20130613174727/http://www.esk.com/uploads/tx_userjspresseveroeff/PR_0712_CFI_12-2007_Hexagonales-BN_e_01.pdf| url-status = live}}</ref><ref name="b1">{{cite book| author = Greim, Jochen| author2 = Schwetz, Karl A.| title = Ullmann's Encyclopedia of Industrial Chemistry|publisher = Wiley-VCH: Weinheim |date = 2005 |doi = 10.1002/14356007.a04_295.pub2| chapter = Boron Carbide, Boron Nitride, and Metal Borides| isbn = 978-3527306732}}</ref>  Molecular analogues of boron nitrides are represented by [[borazine]], (BH)<sub>3</sub>(NH)<sub>3</sub>.{{Citation needed|date=December 2024}}

===Carbides===
[[File:Borfig11a.png|thumb|left|upright=0.7|Unit cell of B<sub>4</sub>C. The green sphere and [[icosahedron|icosahedra]] consist of boron atoms, and black spheres are carbon atoms.<ref name="zhangyb28.5c4">{{cite journal|author=Zhang F X|author2=Xu F F|author3=Mori T|author4=Liu Q L |author5= Sato A|author6=Tanaka T|date=2001|title=Crystal structure of new rare-earth boron-rich solids: REB28.5C4|journal=J. Alloys Compd. |volume=329|issue=1–2|pages=168–172|doi=10.1016/S0925-8388(01)01581-X}}</ref>]]
[[Boron carbide]] is a ceramic material. It is obtained by [[carbothermal reduction]] of B<sub>2</sub>O<sub>3</sub>in an electric furnace:<ref>{{cite book |author=Weimer, Alan W. |url=https://books.google.com/books?id=PC4f40ETjeUC&pg=PA330 |title=Carbide, Nitride and Boride Materials Synthesis and Processing |publisher=Chapman & Hall (London, New York) |year=1997 |isbn=0-412-54060-6 |pages=131}}</ref>
:2 B<sub>2</sub>O<sub>3</sub> + 7 C → B<sub>4</sub>C + 6 CO

Boron carbide's structure is only approximately reflected in its formula of B<sub>4</sub>C, and it shows a clear depletion of carbon from this suggested stoichiometric ratio. This is due to its very complex structure. The substance can be seen with [[empirical formula]] B<sub>12</sub>C<sub>3</sub> (i.e., with B<sub>12</sub> dodecahedra being a motif), but with less carbon, as the suggested C<sub>3</sub> units are replaced with C-B-C chains, and some smaller (B<sub>6</sub>) octahedra are present as well (see the boron carbide article for structural analysis). The repeating polymer plus semi-crystalline structure of boron carbide gives it great structural strength per weight.{{citation needed|date=December 2024}}

===Borides===
[[File:Magnesium-diboride-3D-balls.png|thumb|Ball-and-stick model of superconductor magnesium diboride. Boron atoms lie in hexagonal aromatic graphite-like layers, with a charge of −1 on each boron atom. Magnesium(II) ions lie between layers]]
Binary metal-boron compounds, the metal borides, contain only boron and a metal.  They are metallic, very hard, with high [[melting point]]s.  [[Titanium diboride|TiB<sub>2</sub>]], [[zirconium diboride|ZrB<sub>2</sub>]], and [[Hafnium diboride|HfB<sub>2</sub>]] have melting points above 3000&nbsp;°C.<ref name="b1"/> Some metal borides find specialized applications as hard materials for cutting tools.<ref>{{cite book|chapter-url = https://books.google.com/books?id=PvU-qbQJq7IC&pg=PA638|chapter = Titanium Diboride|pages = 638–639|title = Materials handbook: A concise desktop reference|isbn = 978-1-84628-668-1|author = Cardarelli, François|date = 2008| publisher=Springer |access-date = 5 January 2016|archive-date = 8 January 2017|archive-url = https://web.archive.org/web/20170108051112/https://books.google.com/books?id=PvU-qbQJq7IC&pg=PA638|url-status = live}}</ref>