Rhenium trioxide

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Rhenium trioxide
Properties
Molecular formula	ReO3
Molar mass	234.21 g mol−1
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and 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).

Contents 1 Structure 2 Properties 3 Preparation 4 References

[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 8 (1/8) fragments of Rhenium atoms, and 12 (1/4) fragments of oxygen. 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 it has six neighboring oxygen atoms which bear opposite charge. The coordination number of O in this compound is 2 because it has 2 neighboring 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 resisitivity 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 → 2ReO₃ + CO₂

[edit] References

1. ^ S.J. Heyes (2000) Structures of Simple Inorganic Solids, Department of Chemistry, University of Oxford.
2. ^ ^{a b} Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. , p. 1047.