Praseodymium diiodide
Chemical compound
From Wikipedia, the free encyclopedia
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.
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| Identifiers | |
|---|---|
3D model (JSmol) |
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| 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).
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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.[citation needed] 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:[citation needed]
- 2 PrI2 + 2 H2O → 2 PrOI + H2↑ + 2 HI
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]