Actinium compounds

Actinium compounds are compounds containing the element actinium (Ac). Due to actinium's intense radioactivity, only a limited number of actinium compounds are known. These include: AcF3, AcCl3, AcBr3, AcOF, AcOCl, AcOBr, Ac2S3, Ac2O3, AcPO4 and Ac(NO3)3. Except for AcPO4, they are all similar to the corresponding lanthanum compounds. They all contain actinium in the oxidation state +3.[1][2] In particular, the lattice constants of the analogous lanthanum and actinium compounds differ by only a few percent.[2]

Properties of actinium compounds
Formula color symmetry space group No Pearson symbol a (pm) b (pm) c (pm) Z density,
g/cm3
Ac silvery fcc[3] Fm3m 225 cF4 531.1 531.1 531.1 4 10.07
AcH2 unknown cubic[3] Fm3m 225 cF12 567 567 567 4 8.35
Ac2O3 white[4] trigonal[5] P3m1 164 hP5 408 408 630 1 9.18
Ac2S3 black cubic[6] I43d 220 cI28 778.56 778.56 778.56 4 6.71
AcF3 white[7] hexagonal[2][5] P3c1 165 hP24 741 741 755 6 7.88
AcCl3 white hexagonal[2][8] P63/m 165 hP8 764 764 456 2 4.8
AcBr3 white[2] hexagonal[8] P63/m 165 hP8 764 764 456 2 5.85
AcOF white[9] cubic[2] Fm3m 593.1 8.28
AcOCl white tetragonal[2] 424 424 707 7.23
AcOBr white tetragonal[2] 427 427 740 7.89
AcPO4·0.5H2O unknown hexagonal[2] 721 721 664 5.48

Here a, b and c are lattice constants, No is space group number and Z is the number of formula units per unit cell. Density was not measured directly but calculated from the lattice parameters.

Oxides


Main article: Actinium(III) oxide

Actinium(III) oxide is the only oxide that actinium can form, with the chemical formula Ac2O3. In this compound, actinium is in the oxidation state +3.[1][10] It is similar to the corresponding lanthanum compound, lanthanum(III) oxide. It can be obtained by heating the hydroxide at 500 °C or the oxalate at 1100 °C, in vacuum. Its crystal lattice is isotypic with the oxides of most trivalent rare-earth metals.[2]

Halides

Actinium trifluoride can be produced either in solution or in solid reaction. The former reaction is carried out at room temperature, by adding hydrofluoric acid to a solution containing actinium ions. In the latter method, actinium metal is treated with hydrogen fluoride vapors at 700 °C in an all-platinum setup. Treating actinium trifluoride with ammonium hydroxide at 900–1000 °C yields oxyfluoride AcOF. Whereas lanthanum oxyfluoride can be easily obtained by burning lanthanum trifluoride in air at 800 °C for an hour, similar treatment of actinium trifluoride yields no AcOF and only results in melting of the initial product.[2][9]

AcF3 + 2 NH3 + H2O → AcOF + 2 NH4F

Actinium trichloride is obtained by reacting actinium hydroxide or oxalate with carbon tetrachloride vapors at temperatures above 960 °C. Similar to oxyfluoride, actinium oxychloride can be prepared by hydrolyzing actinium trichloride with ammonium hydroxide at 1000 °C. However, in contrast to the oxyfluoride, the oxychloride could well be synthesized by igniting a solution of actinium trichloride in hydrochloric acid with ammonia.[2]

Reaction of aluminium bromide and actinium oxide yields actinium tribromide:

Ac2O3 + 2 AlBr3 → 2 AcBr3 + Al2O3

and treating it with ammonium hydroxide at 500 °C results in the oxybromide AcOBr.[2]

Other compounds

Actinium hydride was obtained by reduction of actinium trichloride with potassium at 300 °C, and its structure was deduced by analogy with the corresponding LaH2 hydride. The source of hydrogen in the reaction was uncertain.[11]

Mixing monosodium phosphate (NaH2PO4) with a solution of actinium in hydrochloric acid yields white-colored actinium phosphate hemihydrate (AcPO4·0.5H2O), and heating actinium oxalate with hydrogen sulfide vapors at 1400 °C for a few minutes results in a black actinium sulfide Ac2S3. It may possibly be produced by acting with a mixture of hydrogen sulfide and carbon disulfide on actinium oxide at 1000 °C.[2]

See also

References
  1. Actinium, Great Soviet Encyclopedia (in Russian)
  2. Fried, Sherman; Hagemann, French; Zachariasen, W. H. (1950). "The Preparation and Identification of Some Pure Actinium Compounds". Journal of the American Chemical Society. 72 (2): 771–775. doi:10.1021/ja01158a034.
  3. Farr, J.; Giorgi, A. L.; Bowman, M. G.; Money, R. K. (1961). "The crystal structure of actinium metal and actinium hydride". Journal of Inorganic and Nuclear Chemistry. 18: 42–47. doi:10.1016/0022-1902(61)80369-2. OSTI 4397640.
  4. Stites, Joseph G.; Salutsky, Murrell L.; Stone, Bob D. (1955). "Preparation of Actinium Metal". J. Am. Chem. Soc. 77 (1): 237–240. doi:10.1021/ja01606a085.
  5. Zachariasen, W. H. (1949). "Crystal chemical studies of the 5f-series of elements. XII. New compounds representing known structure types". Acta Crystallographica. 2 (6): 388–390. doi:10.1107/S0365110X49001016.
  6. Zachariasen, W. H. (1949). "Crystal chemical studies of the 5f-series of elements. VI. The Ce2S3-Ce3S4 type of structure" (PDF). Acta Crystallographica. 2: 57–60. doi:10.1107/S0365110X49000126. Archived (PDF) from the original on 2022-10-09.
  7. Meyer, p. 71
  8. Zachariasen, W. H. (1948). "Crystal chemical studies of the 5f-series of elements. I. New structure types". Acta Crystallographica. 1 (5): 265–268. doi:10.1107/S0365110X48000703.
  9. Meyer, pp. 87–88
  10. Sherman, Fried; Hagemann, French; Zachariasen, W. H. (1950). "The Preparation and Identification of Some Pure Actinium Compounds". Journal of the American Chemical Society. 72 (2): 771–775. doi:10.1021/ja01158a034.
  11. Meyer, p. 43
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