{{Short description|Ion}}
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 470604503
| ImageFileL1 = Tetrahydroxyborate-2D-dimensions.png
| ImageFileL1_Ref = {{chemboximage|correct|??}}
| ImageSizeL1 =
| ImageNameL1 = Stereo, skeletal formula of tetrahydroxyborate with a dimension
| ImageFileR1 = Tetrahydroxyborate-anion-from-sodium-salt-xtal-3D-balls.png
| ImageFileR1_Ref = {{chemboximage|correct|??}}
| ImageSizeR1 =
| ImageNameR1 = Ball and stick model of tetrahydroxyborate
| IUPACName = Tetrahydroxyborate
| SystematicName = Tetrahydroxyboranuide<ref name=CHEBI.41132/><br />
Tetrahydroxidoborate(1-)<ref name=CHEBI.41132 />
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|changed|??}}
| CASNo = 15390-83-7
| PubChem = 177595
| ChemSpiderID = 154612
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 41132
| ChEMBL = 1231419
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| Gmelin = 1966
| SMILES = O[B-](O)(O)O
| StdInChI = 1S/BH4O4/c2-1(3,4)5/h2-5H/q-1
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = KCFLOKKYWBPKFN-UHFFFAOYSA-N
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
}}
|Section2={{Chembox Properties
| Formula = [H<sub>4</sub>BO<sub>4</sub>]<sup>−</sup>
| MolarMass = 78.840 g mol<sup>−1</sup>
}}
}}

'''Tetrahydroxyborate''' is an [[inorganic chemistry|inorganic]] [[ion|anion]] with the [[chemical formula]] {{chem2|[BH4O4]−}} or {{chem2|[B(OH)4]−}}. It contributes no colour to tetrahydroxyborate salts. It is found in the mineral [[hexahydroborite]], {{chem2|Ca(B(OH)4)2}}{{hydrate|2}}, originally formulated {{chem2|CaB2O4}}{{hydrate|6}}.<ref name=jack2005/>  It is one of the [[boron]] [[oxyanion|oxoanion]]s, and acts as a [[weak base]]. The [[systematic name]]s are '''tetrahydroxyboranuide''' (substitutive) and '''tetrahydroxidoborate(1−)''' (additive).<ref name=CHEBI.41132/>

== Structure ==

Tetrahydroxyborate has a symmetric [[tetrahedral molecular geometry|tetrahedral]] [[molecular geometry|geometry]],<ref name=GandE/>{{rp|p.203–205}} [[isoelectronic]] with the hypothetical compound [[orthocarbonic acid]]  {{chem2|C(OH)4}}.

== Chemical properties ==

=== Basicity ===

Tetrahydroxyborate act as a weak [[Brønsted–Lowry base]] because it can assimilate a [[proton]] ({{chem2|H+}}), yielding  [[boric acid]] with release of water:
:{{chem2|B(OH)4(-)}} + {{H+}} {{Eqm}} {{chem2|B(OH)3}} + {{chem2|H2O}}
It can also release a [[hydroxy]] anion {{chem2|HO-}}, thus acting as a classical [[Arrhenius base]]:
:{{chem2|B(OH)4(-)}} {{Eqm}} {{chem2|B(OH)3}} + {{OH-}} (pK = 9.14 to the left){{Citation needed|date=March 2016}}
Thus, when boric acid is dissolved in pure (neutral) water, most of it will exist as tetrahydroxyborate ions.{{Citation needed|date=March 2016}}


===With diols===

In aqueous solution, the [[tetrahydroxyborate]] anion reacts with [[cis–trans isomerism|cis]]-[[diol#Vicinal diols|vicinal diols]] ([[organic compound]]s containing similarly-oriented [[hydroxyl]] groups in adjacent [[carbon]] atoms), {{chem2|(R1,R2)\dC(OH)\sC(OH)\d(R3,R4)}}) such as [[mannitol]], [[sorbitol]], [[glucose]] and [[glycerol]], to form
anion esters containing one or two five-member {{chem2|\sB\sO\sC\sC\sO\s}} rings.

For example, the reaction with mannitol can be written as
: {{chem2|[B(OH)4]-}} + {{chem2|H(HCOH)6H}} {{Eqm}} {{chem2|[B(OH)2(H(HCOH)2(HCO\s)2(HCOH)  )]-}} + 2 {{chem2|H2O}} 
: {{chem2|[B(OH)2(H(HCOH)2(HCO\s)2(HCOH)2H)]-}} + {{chem2|H(HCOH)6H}} {{Eqm}} {{chem2|[B(H(HCOH)2(HCO\s)2(HCOH)2H)2]-}} + 2 {{chem2|H2O}}
Giving the overall reaction 
: {{chem2|[B(OH)4]-}} + 2 {{chem2|H(HCOH)6H}} {{Eqm}} [B(H(HCOH)2(HCO\s)2(HCOH)2H)2]-}} + 4 {{chem2|H2O}}

These [[mannitoborate]] esters are fairly stable and thus depletes the [[tetrahydroxyborate]] from the solution.<ref name=NIST1969/><ref name=vogelP357/><ref name=GandE/>

The addition of mannitol to an initially neutral solution containing boric acid or borates lowers the [[pH]] enough for the be titrated by a strong base as NaOH, including with an automated a potentiometric [[titrator]].  This is a reliable method to assay the amount of borate content present in the solution.<ref name=GandE/>

=== Other chemical reactions ===

Upon treatment with a strong acid acid, a metal tetrahydroxyborate converts to [[boric acid]] and the metal salt.

Oxidation of tetrahydroxyborate gives the [[perborate]] anion {{chem2|[B2O4(OH)4](2-)}}:
: 2{{chem2|[B(OH)4]-}} + 2{{chem2|O}} → {{chem2|[B2O4(OH)4](2-)}} + 2{{chem2|H2O}}

When heated to a high temperature, tetrahydroxyborate salts decompose to produce [[metaborate]] salts and water, or to produce boric acid and a metal [[hydroxide]]:
:''n'' {{chem2|[B(OH)4]-}} → ({{chem2|([BO2]−)_{''n''}{}}}) + 2''n''&nbsp;{{chem2|H2O}}
:{{chem2|[B(OH)4]-}} → {{chem2|B(OH)3}} + HO<sup>−</sup>

== Production ==

Tetrahydroxyborate salts are produced by treating boric acid with an [[alkali]] such as [[sodium hydroxide]], with [[catalysis|catalytic]] amounts of water. Other borate salts may be obtained by altering the process conditions.

== Uses ==

Tetrahydroxyborate can be used as a cross-link in polymers.

== Occurrence ==

The tetrahydroxyborate [[anion]] is found in Na[B(OH)<sub>4</sub>],<ref name=cset1993/> Na<sub>2</sub>[B(OH)<sub>4</sub>]Cl and Cu<sup>II</sup>[B(OH)<sub>4</sub>]Cl.

<gallery widths=200>
File:Sodium-tetrahydroxyborate-xtal-3D-balls.png|[[ball-and-stick model]] of the crystal<br>structure of sodium tetrahydroxyborate
File:Sodium-tetrahydroxyborate-xtal-3D-SF.png|[[space-filling model]] of the crystal<br>structure of sodium tetrahydroxyborate
</gallery>

== See also ==

* [[Borate]]
* [[Tetrafluoroborate]]

== References ==

<references>

<ref name=CHEBI.41132>{{Cite web|title = Tetrahydroxoborate(1−) (CHEBI:41132)|url = https://www.ebi.ac.uk/chebi/searchId.do?chebiId=41132|work = Chemical Entities of Biological Interest (ChEBI)|location = UK|publisher = European Bioinformatics Institute}}</ref>

<ref name=jack2005>Glossary of Geology,5th edition, 2005, {{ISBN|978-0922152766}}  ed. by Julia A. Jackson, James P. Mehl, Klaus K. E. Neuendorf, American Geological Institute</ref>

<ref name=cset1993>{{ cite journal | journal = Acta Crystallographica C | volume = 49 | issue = 6 |date=June 1993 | pages = 1039–1041 | title = Structure of sodium tetrahydroxyborate |author1=L. J. Csetenyi |author2=F. P. Glasser |author3=R. A. Howie | doi = 10.1107/S0108270193000058 }}</ref>

<ref name=vogelP357>{{VogelQuantitative6th|page=357}}.</ref>

<ref name=NIST1969>{{Cite book |publisher = U.S. Government Printing Office |title = NIST Special Publication |date = 1969}}</ref>

<ref name=GandE>{{Greenwood&Earnshaw}}</ref>

</references>

[[Category:Borates]]
[[Category:Anions]]