Americium compounds

Three americium oxides are known, with the oxidation states +2 (AmO), +3 ({{chem2|Am2O3}}), and +4 ({{chem2|AmO2}}). Americium(II) oxide was prepared in minute amounts and has not been characterized in detail.{{cite journal |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. |doi=10.1016/0022-1902(67)80191-X}} Americium(III) oxide is a red-brown solid with a melting point of 2205 °C.Wiberg, p. 1972 Americium(IV) oxide is the main form of solid americium which is used in nearly all its applications. Like most other actinide dioxides, it is a black solid with a cubic (fluorite) crystal structure.Greenwood, p. 1267

The oxalate of americium(III), vacuum dried at room temperature, has the chemical formula {{chem2|Am2(C2O4)3*7H2O}}. Upon heating in vacuum, it loses water at 240 °C and starts decomposing into {{chem2|AmO2}} at 300 °C, the decomposition completes at about 470 °C.Penneman, p. 4 The initial oxalate dissolves in nitric acid with the maximum solubility of 0.25 g/L.Penneman, p. 5

Halides of americium are known for the oxidation states +2, +3, and +4,Wiberg, p. 1969 where the +3 is most stable, especially in solutions.{{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 |date=1965 |volume=4 |page=985 |issue=7 |s2cid=96551460 |doi=10.1021/ic50029a013 |url=https://digital.library.unt.edu/ark:/67531/metadc1035960/}}

Reduction of Am(III) compounds with sodium amalgam yields Am(II) salts – the black halides {{chem2|AmCl2}}, {{chem2|AmBr2}}, and {{chem2|AmI2}}. 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 {{chem2|AmCl2}}: 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 {{chem2|AmBr2}}: a = {{val|1159.2|0.4|u=pm}} and c = {{val|712.1|0.3|u=pm}}.{{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 |issue=2 |date=1973 |doi=10.1016/0022-1902(73)80560-3}} They can also be prepared by reacting metallic americium with an appropriate mercury halide {{chem2|HgX2}}, where X = Cl, Br, or I:Greenwood, p. 1272

:{{chem2|Am + HgX2 (mercury halide) → AmX2 + Hg}} (at 400–500 °C)

Americium(III) fluoride ({{chem2|AmF3}}) is poorly soluble and precipitates upon reaction of {{chem2|Am3+}} and fluoride ions in weak acidic solutions:

:{{chem2|Am3+ + 3F- → AmF3↓}}

The tetravalent americium(IV) fluoride ({{chem2|AmF4}}) is obtained by reacting solid americium(III) fluoride with molecular fluorine:{{cite journal |title=New Compounds of Quadrivalent Americium, AmF₄, KAmF₅ |last1=Asprey |first1=L. B. |journal=Journal of the American Chemical Society |volume=76 |page=2019 |issue=7 |date=1954 |doi=10.1021/ja01636a094|bibcode=1954JAChS..76.2019A }}Greenwood, p. 1271

:{{chem2|2AmF3 + F2 → 2AmF4}}

Another known form of solid tetravalent americium fluoride is {{chem2|KAmF5}}.Penneman, p. 6 Tetravalent americium has also been observed in the aqueous phase. For this purpose, black {{chem2|Am(OH)4}} was dissolved in 15-M {{chem2|NH4F}} with the americium concentration of 0.01 M. The resulting reddish solution had a characteristic optical absorption spectrum which is similar to that of {{chem2|AmF4}} but differed from other oxidation states of americium. Heating the Am(IV) solution to 90 °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.{{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 |issue=9 |date=1961 |doi=10.1021/ja01470a040|bibcode=1961JAChS..83.2200A }}

Most americium(III) halides form hexagonal crystals with slight variation of the color and exact structure between the halogens. So, chloride ({{chem2|AmCl3}}) is reddish and has a structure isotypic to uranium(III) chloride (space group P6₃/m) and the melting point of 715 °C. The fluoride is isotypic to {{chem2|LaF3}} (space group P6₃/mmc) and the iodide to {{chem2|BiI3}} (space group R{{overline|3}}). The bromide is an exception with the orthorhombic {{chem2|PuBr3}}-type structure and space group Cmcm. Crystals of americium chloride hexahydrate ({{chem2|AmCl3*6H2O}}) 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.{{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}}

Oxyhalides of americium in the form {{chem2|Am^{VI}O2X2}}, {{chem2|Am^{V}O2X}}, {{chem2|Am^{IV}OX2}}, and {{chem2|Am^{III}OX}} can be obtained by reacting the corresponding americium halide with oxygen or {{chem2|Sb2O3}}, and AmOCl can also be produced by vapor phase hydrolysis:

:{{chem2|AmCl3 + H2O → AmOCl + 2HCl}}

{{Main article|Americium(III) hydroxide}}

The only known hydroxide of americium is americium(III) hydroxide, which is the first compound of americium, discovered in 1944 as part of the Manhattan project. Americium hydroxide is a pink solid{{cite book |last1=Krivovichev |first1=Sergey |last2=Burns |first2=Peter |last3=Tananaev |first3=Ivan |title=Structural Chemistry of Inorganic Actinide Compounds |year=2006 |publisher=Elsevier |page=67 |isbn=978-0-08-046791-7 |url=https://books.google.com/books?id=mV-phntexBQC&pg=PA67}} which is sparingly soluble in water.{{citation |last=Runde |first=Wolfgang |title=Americium and Curium: Radionuclides |encyclopedia=Encyclopedia of Inorganic and Bioinorganic Chemistry |publisher=American Cancer Society |language=en |isbn=978-1-119-95143-8 |doi=10.1002/9781119951438.eibc0438 |date=2011 |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/9781119951438.eibc0438 |access-date=2020-03-21|url-access=subscription }}

Due to self-irradiation, the crystal structure of {{chem2|^{241}Am(OH)3}} decomposes within 4 to 6 months ({{chem2|^{241}Am}} has a half-life of 432.2 years); for {{chem2|^{244}Cm(OH)3|link=curium hydroxide}} the same process takes less than a day ({{chem2|^{244}Cm}} has a half-life of 18.11 years).

When ozone is bubbled through a slurry of americium(III) hydroxide in 0.03 M potassium bicarbonate at 92 °C, hexagonal {{chem2|KAmO2CO3}} (potassium dioxoamericium(V) carbonate) can be obtained. Potassium carbonate can also be used. The resulting {{chem2|KAmO2CO3}} reacts with dilute acids to produce americium dioxide:{{cite tech report |last1=Penneman |first1=R. A. |last2=Keenan |first2=T. K. |title=The Radiochemistry of Americium and Curium |date=1960-01-01 |osti=4187189 |doi=10.2172/4187189 |url=https://www.osti.gov/biblio/4187189}}

:{{chem2|O3 + Am(OH)3 + KHCO3 + H2O → KAmO2CO3 + 3H2O + O2}}

The known chalcogenides of americium include the sulfide {{chem2|AmS2}},{{cite journal |last1=Damien |first1=D. |title=Americium disulfide and diselenide |journal=Inorganic and Nuclear Chemistry Letters |volume=7 |page=685 |issue=7 |last2=Jove |first2=J. |doi=10.1016/0020-1650(71)80055-7 |date=1971}} selenides {{chem2|AmSe2}} and {{chem2|Am3Se4}},{{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 |issue=11 |date=1974 |doi=10.1016/0022-1902(74)80466-5}} and tellurides {{chem2|Am2Te3}} and {{chem2|AmTe2}}.{{cite journal |last1=Damien |first1=D. |title=Americium tritelluride and ditelluride |journal=Inorganic and Nuclear Chemistry Letters |volume=8 |page=501 |issue=5 |date=1972 |doi=10.1016/0020-1650(72)80262-9}} The pnictides of americium (²⁴³Am) of the AmX type are known for the elements phosphorus, arsenic,{{cite journal |last1=Charvillat |first1=J. |title=Americium monoarsenide |journal=Inorganic and Nuclear Chemistry Letters |volume=9 |page=559 |issue=5 |last2=Damien |first2=D. |date=1973 |doi=10.1016/0020-1650(73)80191-6}} antimony, and bismuth. They crystallize in the rock-salt lattice.

Americium monosilicide (AmSi) and "disilicide" (nominally {{chem2|AmSi_{x}|}}, with 1.87 < x < 2.0) were obtained by reduction of americium(III) fluoride with elementary silicon in vacuum at 1050 °C (AmSi) and 1150−1200 °C ({{chem2|AmSi_{x}|}}). AmSi is a black solid isomorphic with LaSi, it has an orthorhombic crystal symmetry. {{chem2|AmSi_{x}|}} has a bright silvery lustre and a tetragonal crystal lattice (space group I4₁/amd), it is isomorphic with {{chem2|PuSi2}} and {{chem2|ThSi2}}.{{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}} Borides of americium include {{chem2|AmB4}} and {{chem2|AmB6}}. The tetraboride can be obtained by heating an oxide or halide of americium with magnesium diboride in vacuum or inert atmosphere.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{{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 |issue=2 |doi=10.1016/0022-1902(69)80480-X |date=1969}}

{{See also|Organoactinide chemistry}}

File:Uranocene-3D-balls.png

Analogous to uranocene, americium forms the organometallic compound amerocene with two cyclooctatetraene ligands, with the chemical formula {{chem2|(\h{8}C8H8)2Am}},{{cite book |last=Elschenbroich |first=Christoph |title=Organometallchemie |publisher=Vieweg+teubner Verlag |isbn=978-3-8351-0167-8 |page=589 |date=2008}} but it is still hypothetical up to date. An anionic complex KAm(COT)₂ can be prepared by reacting K₂COT and AmI₃ in THF.Mueller, Werner; Lindner, Roland. Potassium bis(cyclooctatetraenyl)americium(III). Transplutonium 1975, Proc. Int. Transplutionium Elem. Symp., 4th [Conference]. 1976. pp 131-137. A cyclopentadienyl complex is also known that is likely to be stoichiometrically {{chem2|AmCp3}}.{{cite book |author=Albrecht-Schmitt, Thomas E. |author-link=Thomas Albrecht-Schönzart |title=Organometallic and Coordination Chemistry of the Actinides |publisher=Springer |isbn=978-3-540-77836-3 |page=8 |date=2008 |url=https://books.google.com/books?id=rgmnVSzFzXMC&pg=PA8}}{{cite journal |last1=Dutkiewicz |first1=Michał S. |last2=Apostolidis |first2=Christos |last3=Walter |first3=Olaf |last4=Arnold |first4=Polly L. |title=Reduction chemistry of neptunium cyclopentadienide complexes: from structure to understanding |journal=Chemical Science |volume=2017 |issue=8 |pages=2553–61 |pmid=28553487 |pmc=5431675 |date=30 January 2017 |doi=10.1039/C7SC00034K}}

Formation of the complexes of the type {{chem2|Am(n\sC3H7\sBTP)3}}, where BTP stands for 2,6-di(1,2,4-triazin-3-yl)pyridine, in solutions containing {{chem2|n\sC3H7\sBTP-}} and {{chem2|Am3+}} 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.{{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 |pmid=20849125 |doi=10.1021/ic101309j |date=2010 |url=https://www.escholar.manchester.ac.uk/api/datastream?publicationPid=uk-ac-man-scw:209191&datastreamId=POST-PEER-REVIEW-PUBLISHERS.PDF}}

• Europium compounds
• Curium compounds

{{Reflist}}

{{Americium compounds}}

Category:Americium

Category:Americium compounds

Category:Chemical compounds by element