Editing Gadolinium (section)

===Chemical properties===
{{Category see also|Gadolinium compounds}}
Gadolinium combines with most elements to form Gd(III) derivatives. It also combines with nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon, and [[arsenic]] at elevated temperatures, forming binary compounds.<ref name="Wiberg">{{Holleman&Wiberg}}</ref>

Unlike the other rare-earth elements, metallic gadolinium is relatively stable in dry air. However, it [[tarnish]]es quickly in moist air, forming a loosely-adhering [[gadolinium(III) oxide]] ({{chem2|Gd2O3}}):
:{{chem2|4 Gd + 3 O2 → 2 Gd2O3}},
which [[spall#Corrosion|spalls]] off, exposing more surface to oxidation.

Gadolinium is a strong [[reducing agent]], which reduces oxides of several metals into their elements. Gadolinium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form [[gadolinium(III) hydroxide]] ({{chem2|Gd(OH)3}}):
:{{chem2|2 Gd + 6 H2O → 2 Gd(OH)3 + 3 H2}}.

Gadolinium metal is attacked readily by dilute [[sulfuric acid]] to form solutions containing the colorless Gd(III) ions, which exist as {{chem2|[Gd(H2O)9](3+)}} complexes:<ref>{{cite web |url= https://www.webelements.com/gadolinium/chemistry.html |title= Chemical reactions of Gadolinium |date= 1993–2018|author= Mark Winter|publisher= The University of Sheffield and WebElements |access-date=6 June 2009}}</ref>
:{{chem2|2 Gd + 3 H2SO4 + 18 H2O → 2 [Gd(H2O)9](3+) + 3 SO4(2-) + 3 H2}}.

====Chemical compounds====
In the great majority of its compounds, like many [[rare-earth metals]], gadolinium adopts the [[oxidation state]] +3. However, gadolinium can be found on rare occasions in the 0, +1 and +2 oxidation states. All four trihalides are known. All are white, except for the iodide, which is yellow. Most commonly encountered of the halides is [[gadolinium(III) chloride]] ({{chem2|GdCl3}}). The oxide dissolves in acids to give the salts, such as [[gadolinium(III) nitrate]].

Gadolinium(III), like most lanthanide ions, forms [[coordination complex|complexes]] with high [[coordination number]]s. This tendency is illustrated by the use of the chelating agent [[DOTA (chelator)|DOTA]], an octa[[denticity|dentate]] ligand. Salts of [Gd(DOTA)]<sup>−</sup> are useful in [[magnetic resonance imaging]]. A variety of related chelate complexes have been developed, including [[gadodiamide]].

Reduced gadolinium compounds are known, especially in the solid state. Gadolinium(II) halides are obtained by heating Gd(III) halides in presence of metallic Gd in [[tantalum]] containers. Gadolinium also forms the sesquichloride {{chem2|Gd2Cl3}}, which can be further reduced to GdCl by annealing at {{convert|800|C}}. This gadolinium(I) chloride forms platelets with layered graphite-like structure.<ref>{{cite book |page=1128 |url=https://books.google.com/books?id=U3MWRONWAmMC&pg=PA1128 |title= Advanced inorganic chemistry |edition= 6th |author= Cotton |publisher= Wiley-India |date= 2007 |isbn= 978-81-265-1338-3}}</ref>