Praseodymium diiodide

Praseodymium diiodide is a chemical compound with the empirical formula of PrI2, consisting of praseodymium and iodine. It is an electride, with the ionic formula of Pr3+(I−)2e−,[2] and therefore not a true praseodymium(II) compound.

Praseodymium diiodide
Identifiers
Properties
I2Pr
Molar mass 394.71660 g·mol−1
Appearance bronze solid[1][2]
Melting point 758 °C[1][2]
Related compounds
Other cations
 Lanthanum(II) iodide
Cerium(II) iodide
Neodymium(II) iodide
Related compounds
 Praseodymium(III) iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Preparation

Praseodymium diiodide can be obtained by reacting praseodymium(III) iodide with metallic praseodymium at 800 °C to 900 °C in an inert atmosphere:[3]

Pr + 2 PrI3 → 3 PrI2

It can also be obtained by reacting praseodymium with mercury(II) iodide where praseodymium displaces mercury:[3]

Pr + HgI2 → PrI2 + Hg

Praseodymium diiodide was first obtained by John D. Corbett in 1961.[4]

Properties

Praseodymium diiodide is an opaque, bronze-coloured solid with a metallic lustre that is soluble in water.[3] The lustre and very high conductivity can be explained by the formulation {PrIII,2I−,e−}, with one electron per metal centre delocalised in a conduction band.[2]

The compound is extremely hygroscopic, and can only be stored and handled under carefully dried inert gas or under a high vacuum. In air it converts into hydrates by absorbing moisture, but these are unstable and more or less rapidly transform into oxide iodides with the evolution of hydrogen:

2PrI2 + 2H2O → 2PrOI + H2↑ + 2HI

With water, these processes take place much faster.[3]

Praseodymium diiodide has five crystal structures, namely the MoSi2 structure, the hexagonal MoS2 structure, the trigonal MoS2 structure, the cadmium chloride structure and the spinel structure.[5] Praseodymium diiodide with the cadmium chloride structure belongs to the trigonal crystal system, with the space group R3m (No. 166), lattice parameters a = 426.5 pm and c = 2247,1 pm; however, the spinel structure of praseodymium diiodide is cubic,[6] with space group F43 (No. 216), and lattice parameter a = 1239.9 pm.[7]

References
  1. Haynes, William M. (2012). CRC handbook of chemistry and physics : a ready-reference book of chemical and physical data. Boca Raton, Fla.: CRC. p. 84. ISBN 978-1-4398-8049-4. OCLC 793213751.
  2. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1240–1242. ISBN 978-0-08-037941-8.
  3. hrsg. von Georg Brauer. Unter Mitarb. von M. Baudler (1975). Handbuch der präparativen anorganischen Chemie / 1 (in German). Stuttgart: Enke. p. 1081. ISBN 3-432-02328-6. OCLC 310719485.
  4. Meyer, G.; Naumann, Dieter; Wesemann, Lars (2006). Inorganic chemistry in focus. III. Weinheim: Wiley-VCH. p. 45. ISBN 978-3-527-60993-2. OCLC 86225074.
  5. Riedel, Erwin; Alsfasser, Ralf (2007). Moderne anorganische Chemie : mit CD-ROM : [133 Tabellen] (in German). Berlin: Gruyter. p. 366. ISBN 978-3-11-019060-1. OCLC 237200027.
  6. Warkentin, E.; Bärnighausen, H. (1979). "Die Kristallstruktur von Praseodymdiiodid (Modifikation V)". Z. anorg. allg. Chem. 459: 187–200. doi:10.1002/zaac.19794590120.
  7. Gerlitzki, Niels; Meyer, Gerd; Mudring, Anja-Verena; Corbett, John D. (2004). "Praseodymium diiodide, PrI2, revisited by synthesis, structure determination and theory". J. Alloys Compd. Elsevier BV. 380 (1–2): 211–218. doi:10.1016/j.jallcom.2004.03.046. ISSN 0925-8388.
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