Praseodymium diselenide
| Names | |
|---|---|
| Other names
Praseodymium(III) diselenide | |
| Identifiers | |
| Properties | |
| PrSe2 | |
| Molar mass | 298.83 g/mol |
| Structure | |
| Monoclinic, CeSe2 type | |
| P21/a | |
a = 0.8396 nm, b = 0.4184 nm, c = 0.8431 nm α = 90°, β = 90.08°, γ = 90° | |
Formula units (Z) |
4 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Praseodymium diselenide is an inorganic compound of praseodymium and selenium with the formula PrSe2. It is a rare-earth polyselenide containing praseodymium in the +3 oxidation state. Its crystal structure contains both isolated selenide ions and Se22− diselenide units.[1]
Preparation
[edit]Praseodymium diselenide can be prepared from pre-annealed praseodymium–selenium powders by chemical transport using iodine as transport agent.[1] Single crystals were obtained over two weeks in a temperature gradient of about 800 to 600 °C.[1]
Properties
[edit]Structure
[edit]PrSe2 crystallizes in the monoclinic crystal system with the CeSe2 structure type, space group P21/a, with four formula units per unit cell.[1] Its lattice parameters are a = 8.396(2) Å, b = 4.184(1) Å, c = 8.431(2) Å and β = 90.08(4)°.[1] The structure consists of alternating puckered double layers containing praseodymium and selenium atoms and planar selenium layers.[1] Selenium atoms in the planar layers form Se22− dumbbells arranged in a herringbone pattern, with an Se–Se distance of 2.467(1) Å.[1] The bonding can therefore be represented approximately as Pr3+(Se2−)(Se22−)1/2, giving an average selenium oxidation state of −1.5.
Non-stoichiometry
[edit]Praseodymium selenides form a series of selenium-deficient phases between Pr2Se3 and PrSe2. Compositions such as PrSe1.9 and PrSe1.85 are known and show ordered or modulated selenium-vacancy arrangements.[2] In PrSe1.85, the modulation originates from a selenium site-occupancy wave coupled to a charge-density wave in the planar selenium layer.[2] Magnetic measurements across the PrSe2−x series are consistent with essentially trivalent praseodymium.[2]
References
[edit]- 1 2 3 4 5 6 7 Doert, Thomas; Graf, Christian (2005). "Synthesis and crystal structures of PrSe2 and NdSe2". Zeitschrift für anorganische und allgemeine Chemie. 631 (6–7): 1101–1106. doi:10.1002/zaac.200400516.
- 1 2 3 "The Pr2Se3–PrSe2 system: Studies of the phase relationships and the modulated crystal structure of PrSe1.85". Journal of Solid State Chemistry. 180: 202–211. 2007. doi:10.1016/j.jssc.2006.10.013.
