Editing Hydroxide (section)

===Carbon group elements===
Carbon forms no simple hydroxides. The [[hypothetical compound]] C(OH)<sub>4</sub> ([[orthocarbonic acid]] or methanetetrol) is unstable in aqueous solution:<ref>{{Cite journal|last1=Böhm|first1=Stanislav|last2=Antipova|first2=Diana|last3=Kuthan|first3=Josef|date=1997|title=A study of methanetetraol dehydration to carbonic acid|journal=International Journal of Quantum Chemistry|language=en|volume=62|issue=3|pages=315–322|doi=10.1002/(SICI)1097-461X(1997)62:3<315::AID-QUA10>3.0.CO;2-8|issn=1097-461X}}</ref>

:C(OH)<sub>4</sub> → {{chem|HCO|3|−}} + H<sub>3</sub>O<sup>+</sup>
:{{chem|HCO|3|−}} + H<sup>+</sup> {{eqm}} H<sub>2</sub>CO<sub>3</sub>
[[Carbon dioxide]] is also known as carbonic anhydride, meaning that it forms by dehydration of [[carbonic acid]] H<sub>2</sub>CO<sub>3</sub> (OC(OH)<sub>2</sub>).<ref>Greenwood, p.&nbsp;310</ref>

[[Silicic acid]] is the name given to a variety of compounds with a generic formula [SiO<sub>''x''</sub>(OH)<sub>4−2''x''</sub>]<sub>''n''</sub>.<ref>Greenwood, p.&nbsp;346</ref><ref>R. K. Iler, ''The Chemistry of Silica'', Wiley, New York, 1979 {{ISBN|0-471-02404-X}}</ref> Orthosilicic acid has been identified in very dilute aqueous solution. It is a weak acid with p''K''<sub>a1</sub>&nbsp;=&nbsp;9.84, p''K''<sub>a2</sub>&nbsp;=&nbsp;13.2 at 25&nbsp;°C. It is usually written as H<sub>4</sub>SiO<sub>4</sub>, but the formula Si(OH)<sub>4</sub> is generally accepted.<ref name=scdb/>{{dubious|discuss|date=November 2014}} Other silicic acids such as metasilicic acid (H<sub>2</sub>SiO<sub>3</sub>), disilicic acid (H<sub>2</sub>Si<sub>2</sub>O<sub>5</sub>), and pyrosilicic acid (H<sub>6</sub>Si<sub>2</sub>O<sub>7</sub>) have been characterized. These acids also have hydroxide groups attached to the silicon; the formulas suggest that these acids are protonated forms of poly[[oxyanion]]s.

Few hydroxo complexes of [[germanium]] have been characterized. [[Tin(II) hydroxide]] Sn(OH)<sub>2</sub> was prepared in anhydrous media. When [[tin(II) oxide]] is treated with alkali the pyramidal hydroxo complex {{chem|Sn(OH)|3|−}} is formed. When solutions containing this ion are acidified, the ion [Sn<sub>3</sub>(OH)<sub>4</sub>]<sup>2+</sup> is formed together with some basic hydroxo complexes. The structure of [Sn<sub>3</sub>(OH)<sub>4</sub>]<sup>2+</sup> has a triangle of tin atoms connected by bridging hydroxide groups.<ref>Greenwood, p.&nbsp;384</ref> Tin(IV) hydroxide is unknown but can be regarded as the hypothetical acid from which [[stannate]]s, with a formula [Sn(OH)<sub>6</sub>]<sup>2−</sup>, are derived by reaction with the (Lewis) basic hydroxide ion.<ref>Greenwood, pp.&nbsp;383–384</ref>

Hydrolysis of Pb<sup>2+</sup> in aqueous solution is accompanied by the formation of various hydroxo-containing complexes, some of which are insoluble. The basic hydroxo complex [Pb<sub>6</sub>O(OH)<sub>6</sub>]<sup>4+</sup> is a cluster of six lead centres with metal–metal bonds surrounding a central oxide ion. The six hydroxide groups lie on the faces of the two external Pb<sub>4</sub> tetrahedra. In strongly alkaline solutions soluble [[plumbate]] ions are formed, including [Pb(OH)<sub>6</sub>]<sup>2−</sup>.<ref>Greenwood, p.&nbsp;395</ref>