Editing Americium (section)

==Chemical compounds==
{{Main|Americium compounds}}

===Oxygen compounds===
Three americium oxides are known, with the oxidation states +2 (AmO), +3 (Am<sub>2</sub>O<sub>3</sub>) and +4 (AmO<sub>2</sub>). [[Americium(II) oxide]] was prepared in minute amounts and has not been characterized in detail.<ref>{{Cite journal| doi = 10.1016/0022-1902(67)80191-X| title = A note on AmN and AmO| journal = Journal of Inorganic and Nuclear Chemistry| volume = 29| issue = 10| pages = 2650–2652| year = 1967| last1 = Akimoto | first1 = Y.}}</ref> [[Americium(III) oxide]] is a red-brown solid with a melting point of 2205&nbsp;°C.<ref name = "HOWI_1972">Wiberg, p. 1972</ref> [[Americium(IV) oxide]] is the main form of solid americium which is used in nearly all its applications. As most other actinide dioxides, it is a black solid with a cubic ([[fluorite]]) crystal structure.<ref name="g1267">Greenwood, p. 1267</ref>

The oxalate of americium(III), vacuum dried at room temperature, has the chemical formula Am<sub>2</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>·7H<sub>2</sub>O. Upon heating in vacuum, it loses water at 240&nbsp;°C and starts decomposing into AmO<sub>2</sub> at 300&nbsp;°C, the decomposition completes at about 470&nbsp;°C.<ref name="p4" /> The initial oxalate dissolves in nitric acid with the maximum solubility of 0.25&nbsp;g/L.<ref name="p5">Penneman, p. 5</ref>

===Halides===
[[Halide]]s of americium are known for the oxidation states +2, +3 and +4,<ref name="HOWI_1969">Wiberg, p. 1969</ref> where the +3 is most stable, especially in solutions.<ref name="hal1">{{cite journal|title=Crystal Structures of the Trifluorides, Trichlorides, Tribromides, and Triiodides of Americium and Curium|last1=Asprey|first1=L. B.|last2=Keenan|first2=T. K.|last3=Kruse|first3=F. H.|journal=Inorganic Chemistry|volume=4|page=985|date=1965|doi=10.1021/ic50029a013|issue=7|s2cid=96551460 |url=https://digital.library.unt.edu/ark:/67531/metadc1035960/}}</ref>

{| Class ="wikitable" style ="text-align:center;"
|-
! Oxidation state
! F
! Cl
! Br
! I
|-
! +4
| [[Americium(IV) fluoride]] <br /> AmF<sub>4</sub><br /> pale pink
|
|
|
|-
! +3
| [[Americium(III) fluoride]] <br /> AmF<sub>3</sub><br /> pink
| [[Americium(III) chloride]] <br /> AmCl<sub>3</sub><br /> pink
| [[Americium(III) bromide]] <br /> AmBr<sub>3</sub><br /> light yellow
| [[Americium(III) iodide]] <br /> AmI<sub>3</sub><br /> light yellow
|-
! +2
|
| [[Americium(II) chloride]] <br /> AmCl<sub>2</sub><br /> black <!-- (CAS: 16601-54-0) --->
| [[Americium(II) bromide]] <br /> AmBr<sub>2</sub><br /> black <!-- (CAS: 39705-49-2) -->
| [[Americium(II) iodide]] <br /> AmI<sub>2</sub><br /> black <!-- (CAS: 38150-40-2) -->
|}

Reduction of Am(III) compounds with sodium [[Amalgam (chemistry)|amalgam]] yields Am(II) salts – the black halides AmCl<sub>2</sub>, AmBr<sub>2</sub> and AmI<sub>2</sub>. They are very sensitive to oxygen and oxidize in water, releasing hydrogen and converting back to the Am(III) state. Specific lattice constants are:
* [[Orthorhombic]] AmCl<sub>2</sub>: ''a'' = {{val|896.3|0.8|u=pm}}, ''b'' = {{val|757.3|0.8|u=pm}} and ''c'' = {{val|453.2|0.6|u=pm}}
* [[Tetragonal]] AmBr<sub>2</sub>: ''a'' = {{val|1159.2|0.4|u=pm}} and ''c'' = {{val|712.1|0.3|u=pm}}.<ref>{{cite journal|last1=Baybarz|first1=R. D.|title=The preparation and crystal structures of americium dichloride and dibromide|journal=Journal of Inorganic and Nuclear Chemistry|volume=35|page=483|date=1973|doi=10.1016/0022-1902(73)80560-3|issue=2}}</ref> They can also be prepared by reacting metallic americium with an appropriate mercury halide HgX<sub>2</sub>, where X = Cl, Br or I:<ref name="g1272">Greenwood, p. 1272</ref>
: <chem>{Am} + \underset{mercury\ halide}{HgX2} ->[{} \atop 400 - 500 ^\circ \ce C] {AmX2} + {Hg}</chem>

Americium(III) fluoride (AmF<sub>3</sub>) is poorly soluble and precipitates upon reaction of Am<sup>3+</sup> and fluoride ions in weak acidic solutions:

: <chem>Am^3+ + 3F^- -> AmF3(v)</chem>

The tetravalent americium(IV) fluoride (AmF<sub>4</sub>) is obtained by reacting solid americium(III) fluoride with molecular [[fluorine]]:<ref name="f4">{{cite journal|title=New Compounds of Quadrivalent Americium, AmF<sub>4</sub>, KAmF<sub>5</sub>|last1=Asprey|first1=L. B.|journal=Journal of the American Chemical Society|volume=76|page=2019|date=1954|doi=10.1021/ja01636a094|issue=7|bibcode=1954JAChS..76.2019A }}</ref><ref name="g1271">Greenwood, p. 1271</ref>

: <chem>2AmF3 + F2 -> 2AmF4</chem>

Another known form of solid tetravalent americium fluoride is KAmF<sub>5</sub>.<ref name="f4" /><ref name="p6">Penneman, p. 6</ref> Tetravalent americium has also been observed in the aqueous phase. For this purpose, black Am(OH)<sub>4</sub> was dissolved in 15-[[Mole (unit)|M]] NH<sub>4</sub>F with the americium concentration of 0.01 M. The resulting reddish solution had a characteristic optical absorption spectrum which is similar to that of AmF<sub>4</sub> but differed from other oxidation states of americium. Heating the Am(IV) solution to 90&nbsp;°C did not result in its disproportionation or reduction, however a slow reduction was observed to Am(III) and assigned to self-irradiation of americium by alpha particles.<ref name="amoh4">{{cite journal|last1=Asprey|first1=L. B.|title=First Observation of Aqueous Tetravalent Americium1|last2=Penneman|first2=R. A.|journal=Journal of the American Chemical Society|volume=83|page=2200|date=1961|doi=10.1021/ja01470a040|issue=9|bibcode=1961JAChS..83.2200A }}</ref>

Most americium(III) halides form hexagonal crystals with slight variation of the color and exact structure between the halogens. So, chloride (AmCl<sub>3</sub>) is reddish and has a structure isotypic to [[uranium(III) chloride]] (space group P6<sub>3</sub>/m) and the melting point of 715&nbsp;°C.<ref name="HOWI_1969" /> The fluoride is isotypic to LaF<sub>3</sub> (space group P6<sub>3</sub>/mmc) and the iodide to BiI<sub>3</sub> (space group R{{overline|3}}). The bromide is an exception with the orthorhombic PuBr<sub>3</sub>-type structure and space group Cmcm.<ref name="hal1" /> Crystals of americium(III) chloride hexahydrate (AmCl<sub>3</sub>·6H<sub>2</sub>O) can be prepared by dissolving americium dioxide in hydrochloric acid and evaporating the liquid. Those crystals are hygroscopic and have yellow-reddish color and a [[monoclinic]] crystal structure.<ref>{{cite journal|last1=Burns|first1=John H.|last2=Peterson|first2=Joseph Richard|title=Crystal structures of americium trichloride hexahydrate and berkelium trichloride hexahydrate|journal=Inorganic Chemistry|volume=10|page=147|date=1971|doi=10.1021/ic50095a029}}</ref>

Oxyhalides of americium in the form Am<sup>VI</sup>O<sub>2</sub>X<sub>2</sub>, Am<sup>V</sup>O<sub>2</sub>X, Am<sup>IV</sup>OX<sub>2</sub> and Am<sup>III</sup>OX can be obtained by reacting the corresponding americium halide with oxygen or Sb<sub>2</sub>O<sub>3</sub>, and AmOCl can also be produced by vapor phase [[hydrolysis]]:<ref name="g1272" />
: AmCl<sub>3</sub> + H<sub>2</sub>O -> AmOCl + 2HCl

===Chalcogenides and pnictides===
The known [[chalcogenide]]s of americium include the [[sulfide]] AmS<sub>2</sub>,<ref name="AM_S_SE">{{cite journal|last1=Damien|first1=D.|title=Americium disulfide and diselenide|journal=Inorganic and Nuclear Chemistry Letters|volume=7|page=685|date=1971|doi=10.1016/0020-1650(71)80055-7|issue=7|last2=Jove|first2=J.}}</ref> [[selenide]]s AmSe<sub>2</sub> and Am<sub>3</sub>Se<sub>4</sub>,<ref name = "AM_S_SE " /><ref name="AM_METALLIDE">{{cite journal|last1=Roddy|first1=J.|title=Americium metallides: AmAs, AmSb, AmBi, Am3Se4, and AmSe2|journal=Journal of Inorganic and Nuclear Chemistry|volume=36|page=2531|date=1974|doi=10.1016/0022-1902(74)80466-5|issue=11}}</ref> and [[tellurides]] Am<sub>2</sub>Te<sub>3</sub> and AmTe<sub>2</sub>.<ref>{{cite journal|last1=Damien|first1=D.|title=Americium tritelluride and ditelluride|journal=Inorganic and Nuclear Chemistry Letters|volume=8|page=501|date=1972|doi=10.1016/0020-1650(72)80262-9|issue=5}}</ref> The [[pnictides]] of americium (<sup>243</sup>Am) of the AmX type are known for the elements [[phosphorus]], [[arsenic]],<ref>{{cite journal|last1=Charvillat|first1=J.|title=Americium monoarsenide|journal=Inorganic and Nuclear Chemistry Letters|volume=9|page=559|date=1973|doi=10.1016/0020-1650(73)80191-6|issue=5|last2=Damien|first2=D.}}</ref> [[antimony]] and [[bismuth]]. They crystallize in the [[Cubic crystal system|rock-salt]] lattice.<ref name="AM_METALLIDE" />

===Silicides and borides===
Americium [[silicide|monosilicide]] (AmSi) and "disilicide" (nominally AmSi<sub>x</sub> with: 1.87 < x < 2.0) were obtained by reduction of americium(III) fluoride with elementary [[silicon]] in vacuum at 1050&nbsp;°C (AmSi) and 1150−1200&nbsp;°C (AmSi<sub>x</sub>). AmSi is a black solid isomorphic with LaSi, it has an orthorhombic crystal symmetry. AmSi<sub>x</sub> has a bright silvery lustre and a tetragonal crystal lattice (space group ''I''4<sub>1</sub>/amd), it is isomorphic with PuSi<sub>2</sub> and ThSi<sub>2</sub>.<ref>{{cite journal|last1=Weigel|first1=F.|last2=Wittmann|first2=F.|last3=Marquart|first3=R.|title=Americium monosilicide and "disilicide"|journal=Journal of the Less Common Metals|volume=56|page=47|date=1977|doi=10.1016/0022-5088(77)90217-X}}</ref> [[Boride]]s of americium include AmB<sub>4</sub> and AmB<sub>6</sub>. The tetraboride can be obtained by heating an oxide or halide of americium with [[magnesium diboride]] in vacuum or inert atmosphere.<ref>Lupinetti, A. J. ''et al''. {{US patent|6830738}} "Low-temperature synthesis of actinide tetraborides by solid-state metathesis reactions", Filed 4 Apr 2002, Issued 14 December 2004</ref><ref>{{cite journal|last1=Eick|first1=Harry A.|last2=Mulford|first2=R. N. R.|title=Americium and neptunium borides|journal=Journal of Inorganic and Nuclear Chemistry|volume=31|page=371|date=1969|doi=10.1016/0022-1902(69)80480-X|issue=2}}</ref>

===Organoamericium compounds===
[[File:Uranocene-3D-balls.png|thumb|upright=0.55|Predicted structure of amerocene [(η<sup>8</sup>-C<sub>8</sub>H<sub>8</sub>)<sub>2</sub><nowiki>Am]</nowiki>]]
Analogous to [[uranocene]], americium is predicted to form the organometallic compound amerocene with two [[cyclooctatetraene]] ligands, with the chemical formula (η<sup>8</sup>-C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>Am.<ref>{{cite book| last = Elschenbroich| first = Christoph| title = Organometallchemie| date = 2008| publisher = Vieweg+teubner Verlag| isbn = 978-3-8351-0167-8| page = 589 }}</ref> A [[cyclopentadienyl complex]] is also known that is likely to be stoichiometrically AmCp<sub>3</sub>.<ref>{{cite book|author-link=Thomas Albrecht-Schönzart | author = Albrecht-Schmitt, Thomas E. | title = Organometallic and Coordination Chemistry of the Actinides| url = https://books.google.com/books?id=rgmnVSzFzXMC&pg=PA8| date = 2008| publisher = Springer| isbn = 978-3-540-77836-3| page = 8 }}</ref><ref>{{cite journal |last1=Dutkiewicz |first1=Michał S. |last2=Apostolidis |first2=Christos |last3=Walter |first3=Olaf |last4=Arnold |first4=Polly L. |date=30 January 2017 |title=Reduction chemistry of neptunium cyclopentadienide complexes: from structure to understanding |journal=Chemical Science |volume=2017 |issue=8 |pages=2553–61 |doi= 10.1039/C7SC00034K |pmid=28553487 |pmc=5431675 }}</ref>

Formation of the complexes of the type Am(n-C<sub>3</sub>H<sub>7</sub>-BTP)<sub>3</sub>, where BTP stands for 2,6-di(1,2,4-triazin-3-yl)pyridine, in solutions containing n-C<sub>3</sub>H<sub>7</sub>-BTP and Am<sup>3+</sup> ions has been confirmed by [[EXAFS]]. Some of these BTP-type complexes selectively interact with americium and therefore are useful in its selective separation from lanthanides and another actinides.<ref>{{cite journal|last1=Girnt|first1=Denise|last2=Roesky|first2=Peter W.|last3=Geist|first3=Andreas|last4=Ruff|first4=Christian M.|last5=Panak|first5=Petra J.|last6=Denecke|first6=Melissa A.|title=6-(3,5-Dimethyl-1H-pyrazol-1-yl)-2,2'-bipyridine as Ligand for Actinide(III)/Lanthanide(III) Separation|journal=Inorganic Chemistry|volume=49|issue=20|pages=9627–35|date=2010|pmid=20849125|doi=10.1021/ic101309j|url=https://www.escholar.manchester.ac.uk/api/datastream?publicationPid=uk-ac-man-scw:209191&datastreamId=POST-PEER-REVIEW-PUBLISHERS.PDF|archive-date=17 January 2022|access-date=24 August 2019|archive-url=https://web.archive.org/web/20220117094730/https://www.escholar.manchester.ac.uk/api/datastream?publicationPid=uk-ac-man-scw:209191&datastreamId=POST-PEER-REVIEW-PUBLISHERS.PDF|url-status=dead}}</ref>