Editing Gadolinium (section)

====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]] (GdCl<sub>3</sub>). 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 Gd<sub>2</sub>Cl<sub>3</sub>, 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>