Rhenium trioxide
| Rhenium trioxide | |
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Rhenium trioxide |
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Other names
Rhenia |
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| Identifiers | |
| CAS number | 1314-28-9 |
| Properties | |
| Molecular formula | ReO3 |
| Molar mass | 234.205 |
| Appearance | Deep red crystals |
| Density | 6.92 g/cm3 |
| Melting point |
400 °C (decomposes) |
| Refractive index (nD) | 1.68 |
| Structure | |
| Crystal structure | Cubic, cP4 |
| Space group | Pm3m, SpaceGroup = 221 |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Rhenium trioxide (rhenium(VI) oxide, ReO3) is a red solid with a metallic lustre. It is the only stable trioxide of the Group 7 elements (Mn, Tc, Re).
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[edit] Structure
Rhenium oxide forms crystals with a primitive cubic unit cell, with a lattice parameter of 3.742 Å (374.2 pm). The structure of ReO3 is similar to the Perovskite structure (ABO3), without the large A cation at the centre of the unit cell. Each rhenium atom is surrounded by six oxygen atoms, forming a ReO6 octahedron. These octahedra share corners to form the 3-dimensional structure[1].
Upon viewing a unit cell of ReO3, one can see that it is composed of eight ⅛ fragments of rhenium atoms, and twelve ¼ fragments of oxygen atoms. These numbers reduce to 1 Re and 3 O, hence the formula of ReO3. The coordination number of Re in this compound is 6 because each rhenium atom has six neighbouring oxygen atoms which bear opposite charge. The coordination number of O in this compound is 2 because each oxygen atom has 2 neighbouring Re atoms of opposite charge.
[edit] Properties
ReO3 is unusual for an oxide because it exhibits very low resistivity. It behaves more like a metal in that its resistivity decreases as its temperature decreases. At 300 K, its resistivity is 100.0 nΩ·m, whereas at 100 K, this decreases to 6.0 nΩ·m, 17 times less than at 300 K.[2]
[edit] Preparation
Rhenium trioxide can be formed by reducing rhenium(VII) oxide with carbon monoxide[2]:
- Re2O7 + CO → 2 ReO3 + CO2
[edit] References
- ^ S.J. Heyes (2000) Structures of Simple Inorganic Solids, Department of Chemistry, University of Oxford.
- ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419., p. 1047.
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