Berkelium compounds

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Berkelium(IV) oxide

organometallic compounds
.

Oxides

Main article: Berkelium(IV) oxide

Two oxides of berkelium are known, with berkelium in the +3 (Bk2O3) and +4 (BkO2) oxidation states.

pm.[9]

Berkelium(III) oxide, a yellow-green solid, is formed from BkO2 by reduction with hydrogen:

The compound has a melting point of 1920 °C,[10] body-centered cubic crystal lattice and a lattice constant a = 1088.0 ± 0.5 pm.[9] Upon heating to 1200 °C, the cubic Bk2O3 transforms to a monoclinic structure, which further converts to a hexagonal phase at 1750 °C; the latter transition is reversible. Such three-phase behavior is typical for the actinide sesquioxides.[11]

A divalent oxide BkO has been reported as a brittle gray solid with a face centered cubic (fcc) structure and a lattice constant a = 496.4 pm, but its exact chemical composition is uncertain.[11]

Halides

In halides, berkelium assumes the oxidation states +3 and +4.[12] The +3 state is most stable, especially in solutions, and the tetravalent halides BkF4 and Cs2BkCl6 are only known in the solid phase.[13] The coordination of the berkelium atom in its trivalent fluoride and chloride is tricapped trigonal prismatic, with a coordination number of 9. In the trivalent bromide, it is bicapped trigonal prismatic (coordination 8) or octahedral (coordination 6),[14] and in the iodide it is octahedral.[15]

Oxidation number F Cl Br I
+4
Berkelium(IV) fluoride
BkF4
Yellow[15]
 Cs2BkCl6
Orange[11]
+3 Berkelium(III) fluoride
BkF3
Yellow[15] 		Berkelium(III) chloride
BkCl3
Green[15]
Cs2NaBkCl6[16] 		Berkelium(III) bromide[14][17]
BkBr3
Yellow-green[15] 		Berkelium(III) iodide
BkI3
Yellow[15]

Fluorides

Berkelium(IV) fluoride (BkF4) is a yellow-green ionic solid which crystallizes in the

zirconium(IV) fluoride.[16][18][19]

Berkelium(III) fluoride (BkF3) is also a yellow-green solid, but it has two crystalline structures. The most stable phase at low temperatures has an

lanthanum(III) fluoride (Pearson symbol hP24, space group P3c1, No. 165, a = 697 pm, c = 714 pm).[16][18][20]

Chlorides

Main article: Berkelium(III) chloride
Berkelium(III) chloride

Visible amounts of

face-centered cubic structure where Bk(III) ions are surrounded by chloride ions in an octahedral configuration.[24]

The ternary berkelium(IV) chloride Cs2BkCl6 is obtained by dissolving berkelium(IV) hydroxide in a chilled solution of caesium chloride in concentrated hydrochloric acid. It forms orange hexagonal crystals with the lattice constants a = 745.1 pm and c = 1209.7 pm. The average radius of the BkCl62− ion in this compound is estimated as 270 pm.[11]

Bromides and iodides

Two forms of berkelium(III) bromide are known, a monoclinic with berkelium coordination 6 and orthorhombic with coordination 8;

alpha emitter brings undesirable self-damage of the crystal lattice due to the resulting self-heating. This can be avoided by performing measurements as a function of time and extrapolating the obtained results.[13]

Berkelium(III) iodide forms hexagonal crystals with the lattice constants a = 758.4 pm and c = 2087 pm.

tetragonal lattice.[27]

Other inorganic compounds

Pnictides

The mono

pnictides of berkelium-249 are known for the elements nitrogen,[28][29] phosphorus,[29] arsenic[29] and antimony.[29] They are prepared by the reaction of either berkelium(III) hydride (BkH3) or metallic berkelium with these elements at elevated temperatures (about 600 °C) under high vacuum in quartz ampoules. They crystallize in the cubic crystal system with the lattice constant of 495.1 pm for BkN, 566.9 pm for BkP, 582.9 for BkAs and 619.1 pm for BkSb.[29] These lattice constant values are smaller than those in curium pnictides, but are comparable to those of terbium pnictides.[27]

Chalcogenides

Berkelium(III) sulfide, Bk2S3, has been prepared by either treating berkelium oxide with a mixture of hydrogen sulfide and carbon disulfidevapors at 1130 °C, or by directly reacting metallic berkelium with sulfur. These procedures yield brownish-black crystals with a cubic symmetry and lattice constant a = 844 pm.[27]

Other compounds

A solution of berkelium(III) nitrate

Berkelium(III) and berkelium(IV) hydroxides are both stable in 1 M sodium hydroxide solutions. Berkelium(III) phosphate (BkPO4) has been prepared as a solid, which shows strong fluorescence under argon laser (514.5 nm line) excitation.[30] Berkelium hydrides are produced by reacting metal with hydrogen gas at temperatures about 250 °C.[28] They are non-stoichiometric with the nominal formula BkH2+x (0 < x < 1). Whereas the trihydride has a hexagonal symmetry, the dihydride crystallizes in an fcc structure with the lattice constant a = 523 pm.[27] Several other salts of berkelium are known, including Bk2O2S, Bk(NO3)3·4H2O, BkCl3·6H2O, Bk2(SO4)3·12H2O and Bk2(C2O4)3·4H2O.[13] Thermal decomposition at about 600 °C in an argon atmosphere (to avoid oxidation to BkO2) of Bk2(SO4)3·12H2O yields the body-centered orthorhombic crystals of berkelium(IV) oxysulfate (Bk2O2SO4). This compound is thermally stable to at least 1000 °C in an inert atmosphere.[31]

Organoberkelium compounds

Berkelium forms a trigonal (η5–C5H5)3Bk complex with three cyclopentadienyl rings, which can be synthesized by reacting berkelium(III) chloride with the molten beryllocene Be(C5H5)2 at about 70 °C. It has an amber color and orthorhombic symmetry, with the lattice constants of a = 1411 pm, b = 1755 pm and c = 963 pm and the calculated density of 2.47 g/cm3. The complex is stable to heating to at least 250 °C, and sublimates without melting at about 350 °C. The high radioactivity of berkelium gradually destroys the compound within a period of weeks.[21][32] One C5H5 ring in (η5–C5H5)3Bk can be substituted by chlorine to yield [Bk(C5H5)2Cl]2. The optical absorption spectra of this compound are very similar to those of (η5–C5H5)3Bk.[31][33]

Berkelium(III) polyborate(Bk[B6O8(OH)5]), produced by the reaction of berkelium(III) chloride and boric acid, is a yellow solid which is unusual in the fact that the berkelium is covalently pound to the borate, similar to californium(III) polyborate.[34]

See also

References

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  2. ^ a b Peterson, p. 55
  3. doi:10.1021/ic00277a005
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  4. ^ Holleman, p. 1956
  5. ^ Greenwood, p. 1265
  6. ISBN 978-1-4020-3555-5. Archived from the original
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  7. ^ Peterson, p. 45
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  9. ^
    doi:10.1016/0022-1902(68)80352-5
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  10. ^ Holleman, p. 1972
  11. ^ a b c d Peterson, p. 51
  12. ^ a b Holleman, p. 1969
  13. ^ a b c Peterson, p. 47
  14. ^
    doi:10.1021/ic50210a003
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  15. ^ a b c d e f Greenwood, p. 1270
  16. ^ a b c d e Peterson, p. 48
  17. doi:10.1016/0022-1902(75)80532-X
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  18. ^
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  19. doi:10.1021/ic50072a011
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  20. doi:10.1016/0022-1902(68)80353-7
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  21. ^
    doi:10.1021/ic50087a018
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  22. doi:10.1016/0022-1902(68)80443-9
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  23. doi:10.1021/ic00241a015
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  24. ^ a b Peterson, p. 52
  25. doi:10.1021/ic50095a029
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  26. ^ Peterson, p. 38
  27. ^ a b c d Peterson, p. 53
  28. ^
    doi:10.1016/0022-5088(79)90229-7
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  29. ^
    doi:10.1016/0022-1902(80)80390-3
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  30. ^ Peterson, pp. 39–40
  31. ^ a b Peterson, p. 54
  32. ISBN 978-3-8351-0167-8
    , pp. 583–584
  33. ^ Peterson, p. 41
  34. S2CID 206647926
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Bibliography

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