Promethium arsenate
 | |
| Names | |
|---|---|
| Other names
Promethium(III) arsenate | |
| Identifiers | |
| Properties | |
| PmAsO4 | |
| Molar mass | 283.92 g/mol |
| Appearance | Pale violet (hydrated precipitate); pink (anhydrous) |
| Sparingly soluble in water | |
| Structure | |
| Tetragonal, xenotime type | |
| I41/amd, No. 141 | |
a = 0.731 nm, c = 0.643 nm | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Promethium arsenate is an inorganic compound of promethium and the arsenate ion, with the chemical formula PmAsO4. Like all promethium compounds, it is radioactive. Anhydrous PmAsO4 crystallizes in the tetragonal xenotime structure type.[1]
Preparation
[edit]Hydrated promethium arsenate can be precipitated from an aqueous solution of a promethium(III) salt by addition of a soluble arsenate.
The original synthesis used promethium(III) chloride and sodium hydrogen arsenate. A pale-violet precipitate, interpreted as hydrated PmAsO4·xH2O, was obtained.[1]
Anhydrous PmAsO4 was produced by heating the precipitate for approximately 20–57 hours at 800–950 °C.[1]
A precipitation route using promethium nitrate and sodium dihydrogen arsenate has also been reported for rare-earth arsenates.[2]
Properties
[edit]Crystal structure
[edit]Anhydrous promethium arsenate is pink and crystallizes in the tetragonal crystal system with the xenotime structure type, space group I41/amd (No. 141).[1]
Its lattice parameters are approximately a = 7.31 Å and c = 6.43 Å giving c/a ≈ 0.880.[1]
The structure consists of AsO3−4 tetrahedra and eight-coordinate Pm3+ ions, as in other xenotime-type rare-earth arsenates.
PmAsO4 is structurally important within the rare-earth arsenate series. Neodymium arsenate, NdAsO4, crystallizes in the monoclinic monazite structure, whereas PmAsO4 and the arsenates of the smaller rare-earth ions adopt the tetragonal xenotime structure. The structural boundary therefore lies between NdAsO4 and PmAsO4.[1][3]
Although a monazite-type modification of PmAsO4 has sometimes been inferred in older structural discussions, its existence has not been experimentally demonstrated.[3]
Radioactivity
[edit]Promethium has no stable isotopes, so all samples of PmAsO4 are radioactive. Consequently, studies of the compound have generally been limited to small quantities and structural characterization rather than bulk physical-property measurements.
References
[edit]- 1 2 3 4 5 6 Weigel, F.; Scherer, V. (1967). "Die Chemie des Promethiums. IV. Über ternäre Oxide vom Typ PmXO4". Radiochimica Acta. 7: 40–45.
- ↑ Escobar, Marta E.; Baran, Enrique J. (1978). "Precipitation of rare earth arsenates from aqueous solutions". Zeitschrift für Chemie. 18 (11): 418–419.
- 1 2 Kolitsch, Uwe; Holtstam, Dan (2004). "Crystal chemistry of REEXO4 compounds (X = P, As, V). II. Review of REEXO4 compounds and their stability fields". European Journal of Mineralogy. 16: 117–126.