Editing Tungsten (section)

==Chemical compounds==
{{Category see also|Tungsten compounds}}
[[image:JAFYAQ.png|thumb|upright|Structure of W<sub>6</sub>Cl<sub>18</sub> ("tungsten trichloride")]]
Tungsten forms chemical compounds in oxidation states from −2 to +6. Higher oxidation states, always as oxides, are relevant to its terrestrial occurrence and its biological roles, mid-level oxidation states are often associated with [[metal cluster]]s, and very low oxidation states are typically associated with [[metal carbonyl|CO complexes]]. The chemistries of tungsten and [[molybdenum]] show strong similarities to each other, as well as contrasts with their lighter congener, [[chromium]]. The relative rarity of tungsten(III), for example, contrasts with the pervasiveness of the chromium(III) compounds. The highest oxidation state is seen in [[tungsten(VI) oxide]] (WO<sub>3</sub>).<ref name="Holl">{{cite book|publisher=Walter de Gruyter|date=1985|edition=91–100 |pages=1110–1117|isbn=978-3-11-007511-3|title=Lehrbuch der Anorganischen Chemie|first=Arnold F.|last=Holleman|author2=Wiberg, Egon|author3=Wiberg, Nils|language=de|chapter=Mangan}}</ref> Tungsten(VI) oxide is soluble in aqueous [[base (chemistry)|base]], forming tungstate (WO<sub>4</sub><sup>2−</sup>). This [[oxyanion]] condenses at lower [[pH]] values, forming [[polyoxometalate|polyoxotungstate]]s.<ref>{{cite journal|journal = Angewandte Chemie International Edition|volume = 30|pages=34–48|date = 1997|title = Polyoxometalate Chemistry: An Old Field with New Dimensions in Several Disciplines|first1 = Michael T.|last1 = Pope|last2= Müller |first2 = Achim|doi = 10.1002/anie.199100341}}</ref>

The broad range of [[oxidation state]]s of tungsten is reflected in its various chlorides:<ref name="Holl" />
* [[Tungsten(II) chloride]], which exists as the hexamer W<sub>6</sub>Cl<sub>12</sub>
* [[Tungsten(III) chloride]], which exists as the hexamer W<sub>6</sub>Cl<sub>18</sub>
* [[Tungsten(IV) chloride]], WCl<sub>4</sub>, a black solid, which adopts a polymeric structure.
* [[Tungsten(V) chloride]] WCl<sub>5</sub>, a black solid which adopts a dimeric structure.
* [[Tungsten(VI) chloride]] WCl<sub>6</sub>, which contrasts with the instability of MoCl<sub>6</sub>.

[[Organomolybdenum|Organotungsten compound]]s are numerous and also span a range of oxidation states. Notable examples include the trigonal prismatic {{chem2|[[hexamethyltungsten|W(CH3)6]]}} and octahedral {{chem2|[[tungsten hexacarbonyl|W(CO)6]]}}.