Английская Википедия:Americium compounds
Americium compounds are compounds containing the element americium (Am). These compounds can form in the +2, +3, and +4, although the +3 oxidation state is the most common. The +5, +6 and +7 oxidation states have also been reported.
Oxides
Three americium oxides are known, with the oxidation states +2 (AmO), +3 (Шаблон:Chem2), and +4 (Шаблон:Chem2). Americium(II) oxide was prepared in minute amounts and has not been characterized in detail.[1] Americium(III) oxide is a red-brown solid with a melting point of 2205 °C.[2] 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.[3]
The oxalate of americium(III), vacuum dried at room temperature, has the chemical formula Шаблон:Chem2. Upon heating in vacuum, it loses water at 240 °C and starts decomposing into Шаблон:Chem2 at 300 °C, the decomposition completes at about 470 °C.[4] The initial oxalate dissolves in nitric acid with the maximum solubility of 0.25 g/L.[5]
Halides
Halides of americium are known for the oxidation states +2, +3, and +4,[6] where the +3 is most stable, especially in solutions.[7]
| Oxidation state | F | Cl | Br | I |
|---|---|---|---|---|
| +4 | Americium(IV) fluoride Шаблон:Chem2 pale pink |
|||
| +3 | Americium(III) fluoride Шаблон:Chem2 pink |
Americium(III) chloride Шаблон:Chem2 pink |
Americium(III) bromide Шаблон:Chem2 light yellow |
Americium(III) iodide Шаблон:Chem2 light yellow |
| +2 | Americium(II) chloride Шаблон:Chem2 black |
Americium(II) bromide Шаблон:Chem2 black |
Americium(II) iodide Шаблон:Chem2 black |
Reduction of Am(III) compounds with sodium amalgam yields Am(II) salts – the black halides Шаблон:Chem2, Шаблон:Chem2, and Шаблон:Chem2. 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 Шаблон:Chem2: a = Шаблон:Val, b = Шаблон:Val and c = Шаблон:Val
- Tetragonal Шаблон:Chem2: a = Шаблон:Val and c = Шаблон:Val.[8] They can also be prepared by reacting metallic americium with an appropriate mercury halide Шаблон:Chem2, where X = Cl, Br, or I:[9]
- Шаблон:Chem2 (at 400–500 °C)
Americium(III) fluoride (Шаблон:Chem2) is poorly soluble and precipitates upon reaction of Шаблон:Chem2 and fluoride ions in weak acidic solutions:
The tetravalent americium(IV) fluoride (Шаблон:Chem2) is obtained by reacting solid americium(III) fluoride with molecular fluorine:[10][11]
Another known form of solid tetravalent americium fluoride is Шаблон:Chem2.[10][12] Tetravalent americium has also been observed in the aqueous phase. For this purpose, black Шаблон:Chem2 was dissolved in 15-M Шаблон:Chem2 with the americium concentration of 0.01 M. The resulting reddish solution had a characteristic optical absorption spectrum which is similar to that of Шаблон:Chem2 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.[13]
Most americium(III) halides form hexagonal crystals with slight variation of the color and exact structure between the halogens. So, chloride (Шаблон:Chem2) is reddish and has a structure isotypic to uranium(III) chloride (space group P63/m) and the melting point of 715 °C.[6] The fluoride is isotypic to Шаблон:Chem2 (space group P63/mmc) and the iodide to Шаблон:Chem2 (space group RШаблон:Overline). The bromide is an exception with the orthorhombic Шаблон:Chem2-type structure and space group Cmcm.[7] Crystals of americium chloride hexahydrate (Шаблон:Chem2) 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.[14]
Oxyhalides of americium in the form Шаблон:Chem2, Шаблон:Chem2, Шаблон:Chem2, and Шаблон:Chem2 can be obtained by reacting the corresponding americium halide with oxygen or Шаблон:Chem2, and AmOCl can also be produced by vapor phase hydrolysis:[9]
Other inorganic compounds
Hydroxide
The only known hydroxide of americium is [[americium(III) hydroxide|Шаблон:Chem2]], which is the first compound of americium, discovered in 1944 as part of the Manhattan project. Americium hydroxide is a pink solid[15] which is sparingly soluble in water.[16]
Due to self-irradiation, the crystal structure of Шаблон:Chem2 decomposes within 4 to 6 months (Шаблон:Chem2 has a half-life of 432.2 years); for Шаблон:Chem2 the same process takes less than a day (Шаблон:Chem2 has a half-life of 18.11 years).[15]
When ozone is bubbled through a slurry of americium(III) hydroxide in 0.03 M potassium bicarbonate at 92 °C, hexagonal Шаблон:Chem2 (potassium dioxoamericium(V) carbonate) can be obtained. Potassium carbonate can also be used. The resulting Шаблон:Chem2 reacts with dilute acids to produce americium dioxide:[17]
Chalcogenides and pnictides
The known chalcogenides of americium include the sulfide Шаблон:Chem2,[18] selenides Шаблон:Chem2 and Шаблон:Chem2,[18][19] and tellurides Шаблон:Chem2 and Шаблон:Chem2.[20] The pnictides of americium (243Am) of the AmX type are known for the elements phosphorus, arsenic,[21] antimony, and bismuth. They crystallize in the rock-salt lattice.[19]
Silicides and borides
Americium monosilicide (AmSi) and "disilicide" (nominally Шаблон:Chem2, 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 (Шаблон:Chem2). AmSi is a black solid isomorphic with LaSi, it has an orthorhombic crystal symmetry. Шаблон:Chem2 has a bright silvery lustre and a tetragonal crystal lattice (space group I41/amd), it is isomorphic with Шаблон:Chem2 and Шаблон:Chem2.[22] Borides of americium include Шаблон:Chem2 and Шаблон:Chem2. The tetraboride can be obtained by heating an oxide or halide of americium with magnesium diboride in vacuum or inert atmosphere.[23][24]
Organoamericium compounds
Analogous to uranocene, americium forms the organometallic compound amerocene with two cyclooctatetraene ligands, with the chemical formula Шаблон:Chem2,[25] but it is still hypothetical up to date. An anionic complex KAm(COT)2 can be prepared by reacting K2COT and AmI3 in THF.[26] A cyclopentadienyl complex is also known that is likely to be stoichiometrically Шаблон:Chem2.[27][28]
Formation of the complexes of the type Шаблон:Chem2, where BTP stands for 2,6-di(1,2,4-triazin-3-yl)pyridine, in solutions containing Шаблон:Chem2 and Шаблон:Chem2 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.[29]
See also
References
- ↑ Шаблон:Cite journal
- ↑ Wiberg, p. 1972
- ↑ Greenwood, p. 1267
- ↑ Penneman, p. 4
- ↑ Penneman, p. 5
- ↑ 6,0 6,1 Wiberg, p. 1969
- ↑ 7,0 7,1 Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ 9,0 9,1 Greenwood, p. 1272
- ↑ 10,0 10,1 Шаблон:Cite journal
- ↑ Greenwood, p. 1271
- ↑ Penneman, p. 6
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ 15,0 15,1 Шаблон:Cite book
- ↑ Шаблон:Citation
- ↑ Шаблон:Cite tech report
- ↑ 18,0 18,1 Шаблон:Cite journal
- ↑ 19,0 19,1 Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ Lupinetti, A. J. et al. Шаблон:US patent "Low-temperature synthesis of actinide tetraborides by solid-state metathesis reactions", Filed 4 Apr 2002, Issued 14 December 2004
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite book
- ↑ Mueller, Werner; Lindner, Roland. Potassium bis(cyclooctatetraenyl)americium(III). Transplutonium 1975, Proc. Int. Transplutionium Elem. Symp., 4th [Conference]. 1976. pp 131-137.
- ↑ Шаблон:Cite book
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
