Editing Curium (section)

===Chemical===
[[File:Curium-248.png|thumb|A solution of curium|right|150px]]
Curium ion in solution almost always has a +3 [[oxidation state]], the most stable oxidation state for curium.<ref>Penneman, p. 24</ref> A +4 oxidation state is seen mainly in a few solid phases, such as CmO<sub>2</sub> and CmF<sub>4</sub>.<ref>{{cite journal|last1=Keenan|first1=Thomas K.|title=First Observation of Aqueous Tetravalent Curium|journal=Journal of the American Chemical Society|volume=83|issue=17|page=3719|date=1961|doi=10.1021/ja01478a039|bibcode=1961JAChS..83.3719K }}</ref><ref name = "asprey" /> Aqueous curium(IV) is only known in the presence of strong oxidizers such as [[potassium persulfate]], and is easily reduced to curium(III) by [[radiolysis]] and even by water itself.<ref name="Lumetta" /> Chemical behavior of curium is different from the actinides thorium and uranium, and is similar to americium and many [[lanthanide]]s. In aqueous solution, the Cm<sup>3+</sup> ion is colorless to pale green;<ref name="g1265">Greenwood, p. 1265</ref> Cm<sup>4+</sup> ion is pale yellow.<ref name="HOWI_1956">Holleman, p. 1956</ref> The optical absorption of Cm<sup>3+</sup> ion contains three sharp peaks at 375.4, 381.2 and 396.5&nbsp;nm and their strength can be directly converted into the concentration of the ions.<ref>Penneman, pp. 25–26</ref> The +6 oxidation state has only been reported once in solution in 1978, as the curyl ion ({{chem|CmO|2|2+}}): this was prepared from [[beta decay]] of [[americium-242]] in the americium(V) ion {{chem|242|AmO|2|+}}.<ref name="CmO3" /> Failure to get Cm(VI) from oxidation of Cm(III) and Cm(IV) may be due to the high Cm<sup>4+</sup>/Cm<sup>3+</sup> [[ionization energy|ionization potential]] and the instability of Cm(V).<ref name="Lumetta">{{cite book|first1 = Lumetta|last1 = Gregg J.|first2 = Major C.|last2 = Thompson|first3 = Robert A.|last3 = Penneman|first4 = P. Gary|last4 = Eller|contribution = Curium|title = The Chemistry of the Actinide and Transactinide Elements|editor1-first = Lester R.|editor1-last = Morss|editor2-first = Norman M.|editor2-last = Edelstein|editor3-first = Jean|editor3-last = Fuger|edition = 3rd|date = 2006|volume = 3|publisher = Springer|location = Dordrecht, the Netherlands|pages = 1397–1443|url = http://radchem.nevada.edu/classes/rdch710/files/neptunium.pdf|doi = 10.1007/1-4020-3598-5_9|isbn = 978-1-4020-3555-5|access-date = 2013-10-18|archive-date = 2018-01-17|archive-url = https://web.archive.org/web/20180117190715/http://radchem.nevada.edu/classes/rdch710/files/neptunium.pdf|url-status = dead}}</ref>

Curium ions are [[HSAB theory|hard Lewis acids]] and thus form most stable complexes with hard bases.<ref>{{cite journal|last1=Jensen|first1=Mark P.|last2=Bond|first2=Andrew H.|title=Comparison of Covalency in the Complexes of Trivalent Actinide and Lanthanide Cations|journal=Journal of the American Chemical Society|volume=124|issue=33|date=2002|pmid=12175247|doi=10.1021/ja0178620|pages=9870–9877|bibcode=2002JAChS.124.9870J |url=https://figshare.com/articles/Comparison_of_Covalency_in_the_Complexes_of_Trivalent_Actinide_and_Lanthanide_Cations/3640428}}</ref> The bonding is mostly ionic, with a small covalent component.<ref>{{cite journal|last1=Seaborg |first1=Glenn T. |title=Overview of the Actinide and Lanthanide (the ''f'') Elements|journal=Radiochimica Acta|date=1993|volume=61|issue=3–4 |pages=115–122|doi=10.1524/ract.1993.61.34.115 |s2cid=99634366 }}</ref> Curium in its complexes commonly exhibits a 9-fold coordination environment, with a [[tricapped trigonal prismatic molecular geometry]].<ref>Greenwood, p. 1267</ref>