View source for Rhenium trioxide

{{chembox
| Verifiedfields = changed
| Watchedfields  = changed
| verifiedrevid  = 432110388
| Name           = 
| ImageFile      = 
| ImageFileL1    = Rhenium-trioxide-unit-cell-3D-balls-B.png
| ImageFileR1    = REO3.JPG
| ImageSize      = 
| IUPACName      = Rhenium trioxide
| OtherNames     = Rhenia
| SystematicName = 
| Section1       = {{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 1314-28-9
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = FET0Y2C413
| PubChem = 102110
| EINECS = 215-228-8
| SMILES = O=[Re](=O)=O
| InChI = 1S/3O.Re
}}
| Section2       = {{Chembox Properties
| Formula = ReO<sub>3</sub>
| MolarMass = 234.205 g/mol
| Appearance = Deep red crystals
| Density = 6.92 g/cm<sup>3</sup>
| MeltingPtC = 400
| MeltingPt_notes = (decomposes)
| BoilingPt = 
| Solubility = 
| RefractIndex = 1.68
| MagSus = +16.0·10<sup>−6</sup> cm<sup>3</sup>/mol
}}
| Section3       = {{Chembox Structure
| CrystalStruct = Cubic, [[Pearson symbol|cP4]]
| SpaceGroup = P''m<span style="text-decoration: overline">3</span>m'', No. 221
| LattConst_a = 374.8 pm
  }}
| Section4       = 
| Section5       = 
| Section6       = 
| Section7       = {{Chembox Hazards
| MainHazards = 
| FlashPt = 
| AutoignitionPt = 
 }}
}}

'''Rhenium trioxide''' or '''rhenium(VI) oxide''' is an [[inorganic compound]] with the formula ReO<sub>3</sub>.  It is a red solid with a metallic lustre that resembles [[copper]] in appearance. It is the only stable [[trioxide]] of the Group 7 elements ([[Manganese|Mn]], [[Technetium|Tc]], [[Rhenium|Re]]).

==Preparation and structure==
Rhenium trioxide can be formed by reducing [[rhenium(VII) oxide]] with [[carbon monoxide]] at 200&nbsp;°C or elemental [[rhenium]] at 400&nbsp;°C.<ref>H. Nechamkin, C. F. Hiskey, "Rhenium(VI): Oxide (Rhenium Trioxide)" Inorganic Syntheses, 1950 Volume 3, pp. 186-188. {{doi|10.1002/9780470132340.ch49}}</ref>

:Re<sub>2</sub>O<sub>7</sub>  +  CO   →   2 ReO<sub>3</sub>  +  CO<sub>2</sub>
:3 Re<sub>2</sub>O<sub>7</sub>  +  Re   →   7 ReO<sub>3</sub>

Re<sub>2</sub>O<sub>7</sub> can also be reduced with [[dioxane]].<ref name=Glemser/>

[[Image:Rhenium-trioxide-3D-vdW.png|thumb|left|blue: Rhenium, red: Oxygen]]
[[Image:Rhenium trioxide polyhedra.png|thumb|left|ReO<sub>3</sub> polyhedra]]
Rhenium trioxide crystallizes with a [[Primitive cell|primitive]] [[Cubic crystal system|cubic]] [[Crystal structure|unit cell]], with a [[Crystal structure|lattice parameter]] of 3.742 [[Ångström|Å]] (374.2 [[picometre|pm]]). The structure of ReO<sub>3</sub> is similar to that of [[Perovskite (structure)|perovskite]] (ABO<sub>3</sub>), without the large A cation at the centre of the unit cell. Each rhenium center is surrounded by an [[octahedral molecular geometry|octahedron]] defined by six oxygen centers. These octahedra share corners to form the 3-dimensional structure.  The coordination number of O is 2, because each oxygen atom has 2 neighbouring Re atoms.<ref name="G&E1047">{{Greenwood&Earnshaw}}, p. 1047.</ref>

==Properties==
===Physical properties===
ReO<sub>3</sub> is unusual for an oxide because it exhibits very low [[resistivity]]. It behaves like a [[metal]] in that its resistivity decreases as its temperature decreases. At 300 [[Kelvin|K]], its resistivity is 100.0 [[SI electromagnetism units|nΩ·m]], whereas at 100 K, this decreases to 6.0 nΩ·m, 17 times less than at 300 K.<ref name="G&E1047" />

=== Chemical properties ===
Rhenium trioxide is insoluble in water, as well as dilute acids and bases. Heating it in base results in [[disproportionation]] to give {{Chem|ReO|2}} and {{Chem|ReO|4|-}}, while reaction with acid at high temperature affords {{Chem|Re|2|O|7}}. In concentrated nitric acid, it yields [[perrhenic acid]].
Upon heating to 400&nbsp;°C under vacuum, it undergoes [[disproportionation]]:<ref name="Glemser">{{cite book|author1=O. Glemser|author2=R. Sauer|chapter=Rhenium(VI) Oxide|title=Handbook of Preparative Inorganic Chemistry, 2nd Ed. |editor=G. Brauer|publisher=Academic Press|year=1963|place=NY, NY|volume=2pages=1482}}</ref>
: 3 ReO<sub>3</sub>   →   Re<sub>2</sub>O<sub>7</sub>  +   ReO<sub>2</sub>

Rhenium trioxide can be [[Chlorination reaction|chlorinated]] to give [[rhenium trioxide chloride]]:<ref>{{cite book|author1=O. Glemser|author2=R. Sauer|chapter=Rhenium (VII) Oxychloride|title=Handbook of Preparative Inorganic Chemistry, 2nd Ed. |editor=G. Brauer|publisher=Academic Press|year=1963|place=NY, NY|volume=2pages=1480}}</ref>
:{{chem2|2 ReO3 +  Cl2  ->  2 ReO3Cl}}

Rhenium trioxide serves as host for the [[Intercalation (chemistry)|intercalation]] of one and two equivalents of lithium.  Lithium can be incorporated using [[butyl lithium]]:
:{{chem2| ReO3 + C4H9Li -> LiReO3  +  0.5 C8H18 }}
:{{chem2| LiReO3 + C4H9Li -> Li2ReO3  +  0.5 C8H18 }}
Re remains octahedral before and after intercalation, but the framework distorts.<ref>{{cite journal |doi=10.1016/0022-4596(82)90004-4 |title=The Structures of Lithium-Inserted Metal Oxides: LiReO<sub>3</sub> and Li<sub>2</sub>ReO<sub>3</sub> |date=1982 |last1=Cava |first1=R.J. |last2=Santoro |first2=A. |last3=Murphy |first3=D.W. |last4=Zahurak |first4=S. |last5=Roth |first5=R.S. |journal=Journal of Solid State Chemistry |volume=42 |issue=3 |pages=251–262 }}</ref>

==Uses==
===Hydrogenation catalyst===
Rhenium trioxide finds some use in [[organic synthesis]] as a [[catalyst]] for [[amide reduction]].<ref>{{cite book|last1=Nishimura|first1=Shigeo|title=Handbook of Heterogeneous Catalytic Hydrogenation for Organic Synthesis|date=2001|publisher=Wiley-Interscience|location=New York|isbn=9780471396987|pages=408|edition=1st|url=https://books.google.com/books?id=RjZRAAAAMAAJ&q=0471396982}}</ref>

==References==
{{reflist}}
{{Rhenium compounds}}
{{Oxides}}

[[Category:Rhenium compounds]]
[[Category:Hydrogenation catalysts]]
[[Category:Transition metal oxides]]