Promethium compounds

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Promethium compounds are compounds containing the element

cerium group of lanthanides and is chemically very similar to the neighboring elements.[1] Because of its instability, chemical studies of promethium are incomplete. Even though a few compounds have been synthesized, they are not fully studied; in general, they tend to be pink or red in color.[2][3] Treatment of acidic solutions containing Pm3+ ions with ammonia results in a gelatinous light-brown sediment of hydroxide, Pm(OH)3, which is insoluble in water.[4] When dissolved in hydrochloric acid, a water-soluble yellow salt, PmCl3, is produced;[4] similarly, when dissolved in nitric acid, a nitrate results, Pm(NO3)3. The latter is also well-soluble; when dried, it forms pink crystals, similar to Nd(NO3)3.[4] The electron configuration for Pm3+ is [Xe] 4f4, and the color of the ion is pink. The ground state term symbol is 5I4.[5] The sulfate is slightly soluble, like the other cerium group sulfates. Cell parameters have been calculated for its octahydrate; they lead to conclusion that the density of Pm2(SO4)3·8 H2O is 2.86 g/cm3.[6] The oxalate, Pm2(C2O4)3·10 H2O, has the lowest solubility of all lanthanide oxalates.[7]

Unlike the nitrate, the

hexagonal phases, respectively, and the last two phases can be interconverted by adjusting the annealing time and temperature.[8]

Formula symmetry space group No Pearson symbol a (pm) b (pm) c (pm) Z density,
g/cm3
α-Pm dhcp[9][10] P63/mmc 194 hP4 365 365 1165 4 7.26
β-Pm bcc[10] Fm3m 225 cF4 410 410 410 4 6.99
Pm2O3 cubic[8] Ia3 206 cI80 1099 1099 1099 16 6.77
Pm2O3 monoclinic[8] C2/m 12 mS30 1422 365 891 6 7.40
Pm2O3 hexagonal[8] P3m1 164 hP5 380.2 380.2 595.4 1 7.53

Promethium forms only one stable oxidation state, +3, in the form of ions; this is in line with other lanthanides. According to its position in the periodic table, the element cannot be expected to form stable +4 or +2 oxidation states; treating chemical compounds containing Pm3+ ions with strong oxidizing or reducing agents showed that the ion is not easily oxidized or reduced.[1]

Promethium halides[11]
Formula color coordination
number 		symmetry space group No Pearson symbol m.p. (°C)
PmF3 Purple-pink 11 hexagonal P3c1 165 hP24 1338
PmCl3 Lavender 9 hexagonal P63/mc 176 hP8 655
PmBr3 Red 8 orthorhombic Cmcm 63 oS16 624
α-PmI3 Red 8 orthorhombic Cmcm 63 oS16 α→β
β-PmI3 Red 6 rhombohedral R3 148 hR24 695

Bibliography

  • Lavruk︠h︡ina, Avgusta Konstantinovna; Pozdni︠a︡kov, Aleksandr Aleksandrovich (1970). Analytical chemistry of technetium, promethium, astatine and francium.
    S2CID 94160197
    .

References

  1. ^ a b Lavruk︠h︡ina & Pozdni︠a︡kov 1970, p. 120.
  2. ISBN 978-0-19-257046-8
    .
  3. ^ promethium. Encyclopædia Britannica Online
  4. ^ a b c d Lavruk︠h︡ina & Pozdni︠a︡kov 1970, p. 121.
  5. ISBN 978-9056993337
    .
  6. ^ Lavruk︠h︡ina & Pozdni︠a︡kov 1970, p. 122.
  7. ^ Lavruk︠h︡ina & Pozdni︠a︡kov 1970, p. 123.
  8. ^
    doi:10.1111/j.1151-2916.1972.tb11329.x
    .
  9. doi:10.1016/0022-5088(71)90101-9
    .
  10. ^
    ISBN 978-0-8493-0486-6. Archived from the original
    (PDF) on 2012-09-18. Retrieved 2012-06-20.
  11. ISBN 978-0-470-01006-8
    .
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