Editing Germanium (section)

=== Chemistry ===
{{Main|Germanium compounds}}

Elemental germanium starts to oxidize slowly in air at around 250&nbsp;°C, forming [[germanium dioxide|GeO<sub>2</sub>]] .<ref>{{cite journal |doi=10.1016/S0169-4332(98)00251-7 |title=KRXPS study of the oxidation of Ge(001) surface |date=1998 |author=Tabet, N |journal=Applied Surface Science |volume=134 |issue=1–4 |pages=275–282 |bibcode=1998ApSS..134..275T |last2=Salim |first2=Mushtaq A.}}</ref> Germanium is insoluble in dilute [[acids]] and [[alkalis]] but dissolves slowly in hot concentrated sulfuric and nitric acids and reacts violently with molten alkalis to produce [[germanate]]s ({{chem|[GeO|3|]|2−}}). Germanium occurs mostly in the [[oxidation state]] +4 although many +2 compounds are known.<ref name = "Greenwood">{{Greenwood&Earnshaw}}</ref> Other oxidation states are rare: +3 is found in compounds such as Ge<sub>2</sub>Cl<sub>6</sub>, and +3 and +1 are found on the surface of oxides,<ref>{{cite journal |doi=10.1016/S0368-2048(98)00451-4 |title=XPS study of the growth kinetics of thin films obtained by thermal oxidation of germanium substrates |first3=A. L. |last3=Al-Oteibi |first2=M. A. |date=1999 |last2=Salim |author=Tabet, N |journal=Journal of Electron Spectroscopy and Related Phenomena |volume=101–103 |pages=233–238 |bibcode=1999JESRP.101..233T}}</ref> or negative oxidation states in [[germanide]]s, such as −4 in {{chem|Mg|2|Ge}}. Germanium cluster anions ([[Zintl phase|Zintl]] ions) such as Ge<sub>4</sub><sup>2−</sup>, Ge<sub>9</sub><sup>4−</sup>, Ge<sub>9</sub><sup>2−</sup>, [(Ge<sub>9</sub>)<sub>2</sub>]<sup>6−</sup> have been prepared by the extraction from alloys containing alkali metals and germanium in liquid ammonia in the presence of [[ethylenediamine]] or a [[cryptand]].<ref name = "Greenwood" /><ref>{{cite journal |title=Oxidative Coupling of Deltahedral [Ge<sub>9</sub>]<sup>4−</sup> Zintl Ions |first1=Li |last1=Xu |last2=Sevov |first2=Slavi C. |journal=J. Am. Chem. Soc. |date=1999 |volume=121 |issue=39 |pages=9245–9246 |doi=10.1021/ja992269s|bibcode=1999JAChS.121.9245X }}</ref> The oxidation states of the element in these ions are not integers—similar to the [[ozonide]]s O<sub>3</sub><sup>−</sup>.

Two [[oxide]]s of germanium are known: [[germanium dioxide]] ({{chem|GeO|2}}, germania) and [[germanium monoxide]], ({{chem|GeO}}).<ref name="HollemanAF">{{cite book |last=Holleman |first=A. F. |author2=Wiberg, E. |author3=Wiberg, N. |title=Lehrbuch der Anorganischen Chemie |edition=102nd |publisher=de Gruyter |date=2007 |isbn=978-3-11-017770-1 |oclc=145623740}}</ref> The dioxide, GeO<sub>2</sub>, can be obtained by roasting [[germanium disulfide]] ({{chem|GeS|2}}), and is a white powder that is only slightly soluble in water but reacts with alkalis to form [[germanate]]s.<ref name="HollemanAF" /> The monoxide, germanous oxide, can be obtained by the high temperature reaction of GeO<sub>2</sub> with elemental Ge.<ref name="HollemanAF" /> The dioxide (and the related oxides and germanates) exhibits the unusual property of having a high refractive index for visible light, but transparency to [[infrared]] light.<ref>{{cite journal |doi=10.1111/j.1151-2916.2002.tb00594.x |title=Infrared Transparent Germanate Glass-Ceramics |first=Shyam S. |last=Bayya |author2=Sanghera, Jasbinder S. |author3=Aggarwal, Ishwar D. |author4=Wojcik, Joshua A. |journal=Journal of the American Ceramic Society |volume=85 |issue=12 |pages=3114–3116 |date=2002}}</ref><ref>{{cite journal |doi=10.1007/BF00614256 |title=Infrared reflectance and transmission spectra of germanium dioxide and its hydrolysis products |date=1975 |last1=Drugoveiko |first1=O. P. |journal=Journal of Applied Spectroscopy |volume=22 |issue=2 |pages=191–193 |last2=Evstrop'ev |first2=K. K. |last3=Kondrat'eva |first3=B. S. |last4=Petrov |first4=Yu. A. |last5=Shevyakov |first5=A. M. |bibcode=1975JApSp..22..191D |s2cid=97581394}}</ref> [[Bismuth germanate]], Bi<sub>4</sub>Ge<sub>3</sub>O<sub>12</sub> (BGO), is used as a [[scintillator]].<ref name="BGO">{{cite journal |title=A Bismuth Germanate-Avalanche Photodiode Module Designed for Use in High Resolution Positron Emission Tomography |last=Lightstone |first=A. W. |author2=McIntyre, R. J. |author3=Lecomte, R. |author4=Schmitt, D. |journal=IEEE Transactions on Nuclear Science |date=1986 |volume=33 |issue=1 |pages=456–459 |doi=10.1109/TNS.1986.4337142 |bibcode=1986ITNS...33..456L |s2cid=682173}}</ref>

[[Binary compound]]s with other [[chalcogen]]s are also known, such as the [[Germanium disulfide|disulfide]] ({{chem|GeS|2}}) and [[Germanium diselenide|diselenide]] ({{chem|GeSe|2}}), and the [[germanium monosulfide|monosulfide]] (GeS), [[Germanium monoselenide|monoselenide]] (GeSe), and [[Germanium telluride|monotelluride]] (GeTe).<ref name = "Greenwood" /> GeS<sub>2</sub> forms as a white precipitate when hydrogen sulfide is passed through strongly acid solutions containing Ge(IV).<ref name = "Greenwood" /> The disulfide is appreciably soluble in water and in solutions of caustic alkalis or alkaline sulfides. Nevertheless, it is not soluble in acidic water, which allowed Winkler to discover the element.<ref>{{cite journal |first=Otto H. |last=Johnson |title=Germanium and its Inorganic Compounds |journal=Chem. Rev. |date=1952 |volume=51 |issue=3 |pages=431–469 |doi=10.1021/cr60160a002}}</ref> By heating the disulfide in a current of [[hydrogen]], the monosulfide (GeS) is formed, which sublimes in thin plates of a dark color and metallic luster, and is soluble in solutions of the caustic alkalis.<ref name="HollemanAF" /> Upon melting with [[alkali metal compound|alkaline carbonates]] and [[sulfur]], germanium compounds form salts known as thiogermanates.<ref>{{cite journal |doi=10.1039/a703634e |title=First synthesis of mesostructured thiogermanates |date=1997 |last1=Fröba |first1=Michael |journal=Chemical Communications |issue=18 |pages=1729–1730 |last2=Oberender |first2=Nadine}}</ref>

[[File:Germane-2D-dimensions.svg|class=skin-invert-image|upright|left|thumb|Germane is similar to [[methane]].|alt=Skeletal chemical structure of a tetrahedral molecule with germanium atom in its center bonded to four hydrogen atoms. The Ge–H distance is 152.51 picometers.]]
Four tetra[[halides]] are known. Under normal conditions [[Germanium(IV) iodide|germanium tetraiodide]] (GeI<sub>4</sub>) is a solid, [[germanium tetrafluoride]] (GeF<sub>4</sub>) a gas and the others volatile liquids. For example, [[germanium tetrachloride]], GeCl<sub>4</sub>, is obtained as a colorless fuming liquid boiling at 83.1&nbsp;°C by heating the metal with chlorine.<ref name="HollemanAF" /> All the tetrahalides are readily hydrolyzed to hydrated germanium dioxide.<ref name="HollemanAF" /> GeCl<sub>4</sub> is used in the production of organogermanium compounds.<ref name = "Greenwood" /> All four dihalides are known and in contrast to the tetrahalides are polymeric solids.<ref name = "Greenwood" /> Additionally Ge<sub>2</sub>Cl<sub>6</sub> and some higher compounds of formula Ge<sub>''n''</sub>Cl<sub>2''n''+2</sub> are known.<ref name="HollemanAF" /> The unusual compound Ge<sub>6</sub>Cl<sub>16</sub> has been prepared that contains the Ge<sub>5</sub>Cl<sub>12</sub> unit with a [[neopentane]] structure.<ref>{{cite journal |title=The Crystal Structure and Raman Spectrum of Ge<sub>5</sub>Cl<sub>12</sub>·GeCl<sub>4</sub> and the Vibrational Spectrum of Ge<sub>2</sub>Cl<sub>6</sub> |last1=Beattie |first1=I. R. |last2=Jones |first2=P.J. |last3=Reid |first3=G. |author4=Webster, M. |journal=Inorg. Chem. |volume=37 |issue=23 |pages=6032–6034 |date=1998 |doi=10.1021/ic9807341 |pmid=11670739}}</ref>

[[Germane]] (GeH<sub>4</sub>) is a compound similar in structure to [[methane]]. Polygermanes—compounds that are similar to [[alkane]]s—with formula Ge<sub>''n''</sub>H<sub>2''n''+2</sub> containing up to five germanium atoms are known.<ref name = "Greenwood" /> The germanes are less volatile and less reactive than their corresponding silicon analogues.<ref name = "Greenwood" /> GeH<sub>4</sub> reacts with alkali metals in liquid ammonia to form white crystalline MGeH<sub>3</sub> which contain the [[germyl|GeH<sub>3</sub><sup>−</sup>]] [[anion]].<ref name = "Greenwood" /> The germanium hydrohalides with one, two and three halogen atoms are colorless reactive liquids.<ref name = "Greenwood" />

[[File:NucleophilicAdditionWithOrganogermanium.png|class=skin-invert-image|right|thumb|upright=1.25|[[Nucleophile|Nucleophilic]] addition with an organogermanium compound|alt=Skeletal chemical structures outlining an additive chemical reaction including an organogermanium compound.]]
The first [[organogermanium compound]] was synthesized by Winkler in 1887; the reaction of germanium tetrachloride with [[diethylzinc]] yielded [[tetraethylgermane]] ({{chem|Ge(C|2|H|5|)|4}}).<ref name="Winkle2" /> Organogermanes of the type R<sub>4</sub>Ge (where R is an [[alkyl]]) such as [[tetramethylgermane]] ({{chem|Ge(CH|3|)|4}}) and tetraethylgermane are accessed through the cheapest available germanium precursor [[germanium tetrachloride]] and alkyl nucleophiles. Organic germanium hydrides such as [[isobutylgermane]] ({{chem|(CH|3|)|2|CHCH|2|GeH|3}}) were found to be less hazardous and may be used as a liquid substitute for toxic germane gas in [[semiconductor]] applications. Many germanium [[reactive intermediate]]s are known: [[-yl|germyl]] [[free radical]]s, [[germylene]]s (similar to [[carbene]]s), and germynes (similar to [[carbyne]]s).<ref>{{cite journal |title=Reactive intermediates in organogermanium chemistry |first=Jacques |last=Satge |journal=Pure Appl. Chem. |volume=56 |issue=1 |pages=137–150 |date=1984 |doi=10.1351/pac198456010137 |s2cid=96576323 |doi-access=free}}</ref><ref>{{cite journal |title=Organogermanium Chemistry |first=Denis |last=Quane |author2=Bottei, Rudolph S. |journal=Chemical Reviews |volume=63 |issue=4 |pages=403–442 |date=1963 |doi=10.1021/cr60224a004}}</ref> The organogermanium compound [[Propagermanium|2-carboxyethylgermasesquioxane]] was first reported in the 1970s, and for a while was used as a dietary supplement and thought to possibly have anti-tumor qualities.<ref name="toxic" />

Using a ligand called Eind (1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl) germanium is able to form a double bond with oxygen (germanone). Germanium hydride and germanium tetrahydride are very flammable and even explosive when mixed with air.<ref>{{cite news |last=Broadwith |first=Phillip |title=Germanium-oxygen double bond takes centre stage |url=http://www.rsc.org/chemistryworld/News/2012/March/germanone-germanium-oxygen-double-bond-created.asp |access-date=2014-05-15 |newspaper=Chemistry World |date=25 March 2012 |archive-date=2014-05-17 |archive-url=https://web.archive.org/web/20140517121351/http://www.rsc.org/chemistryworld/News/2012/March/germanone-germanium-oxygen-double-bond-created.asp |url-status=live}}</ref>