Uranium hexachloride

Names
IUPAC name

Uranium(VI) chloride

Other names

Uranium hexachloride
Peruranic chloride

Identifiers

CAS Number

* 161280-02-0

3D model (JSmol)

* Interactive image

ChemSpider |

* 57564875

PubChem CID

* 57346050

InChI

* InChI=1S/6ClH.U/h6*1H;/p-6

Key: XFCORTPUZRSUIZ-UHFFFAOYSA-H

SMILES

* [Cl-].[Cl-].[Cl-].[Cl-].[Cl-].[Cl-].[U]

Properties

Chemical formula

| UCl

Molar mass | 450.745 g/mol
Appearance  | dark green crystalline solid
Density | 3600 kg/m3
Melting point |  177 °C (351 °F; 450 K)
Related compounds

Other anions

| Uranium hexafluoride

Other cations

| Tungsten hexachloride

Related uranium chlorides

* Uranium(III) chloride
* Uranium(IV) chloride
* Uranium(V) chloride

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Infobox references

Uranium hexachloride (UCl
6) is an inorganic chemical compound of uranium in the +6 oxidation state.[1][2] UCl
6 is a metal halide composed of uranium and chlorine. It is a multi-luminescent dark green crystalline solid with a vapor pressure between 1-3 mmHg at 373.15 K.[3] UCl
6 is stable in a vacuum, dry air, nitrogen and helium at room temperature. It is soluble in carbon tetrachloride (CCl
4). Compared to the other uranium halides, little is known about UCl

## Contents

* 1 Structure and Bonding
* 2 Chemical properties
* 2.1 Thermal decomposition
* 2.2 Solubility
* 2.3 Reaction with hydrogen fluoride
* 3 Synthesis
* 4 References

## Structure and Bonding

Uranium hexachloride has an octahedral geometry, with point group Oh. Its lattice (dimensions: 10.95 ± 0.02 Å x 6.03 ± 0.01 Å) is hexagonal in shape with three molecules per cell; the average theoretical U-Cl bond is 2.472 Å long (the experimental U-Cl length found by X-ray diffraction is 2.42 Å),[4] and the distance between two adjacent chlorine atoms is 3.65 Å.

## Chemical properties

Uranium hexachloride is a highly hygroscopic compound and decomposes readily when exposed to ordinary atmospheric conditions.[5] therefore it should be handled in either a vacuum apparatus or in a dry box.

### Thermal decomposition

UCl
6 is stable up to temperatures between 120 °C and 150 °C. The decomposition of UCl
6 results in a solid phase transition from one crystal form of UCl
6 to another more stable form.[6] However, the decomposition of gaseous UCl
6 produces UCl
5. The activation energy for this reaction is about 40 kcal per mole.

2 UCl
6 (g) → 2 UCl
5 (s) + Cl
2 (g)

### Solubility

UCl
6 is not a very soluble compound. It dissolves in CCl
4 to give a brown solution. It is slightly soluble in isobutyl bromide and in fluorocarbon (C

16).[6]

Solvents  | Temperature (°C)  | Grams of UCl
6/100g of solution

|
|

CCl
4 | −18  | 2.64
CCl
4 | 0  | 4.9
CCl
4 | 20  | 7.8
6.6% Cl
2 : 93.4% CCl
4 | −20  | 2.4
12.5% Cl
2 : 87.5% CCl
4 | −20  | 2.23
12.5% Cl
2 : 87.5% CCl
4 | 0  | 3.98
Liquid Cl
2 | −33  | 2.20

3Cl | −24  | 1.16
Benzene | 80  | Insoluble
Freon 113  | 45  | 1.83

### Reaction with hydrogen fluoride

When UCl
6 is reacted with purified anhydrous liquid hydrogen fluoride (HF) at room temperature produces UF
5.[6]

2 UCl
6 \+ 10 HF → 2 UF
5 \+ 10 HCl + Cl

## Synthesis

Uranium hexachloride can be synthesized from the reaction of uranium trioxide (UO
3) with a mixture of liquid CCl
4 and hot chlorine (Cl
2). The yield can be increased if the reaction carried out in the presence of UCl
5.[7] The UO
3 is converted to UCl
5, which in turn reacts with the excess Cl
2 to form UCl
6. It requires a substantial amount of heat for the reaction to take place; the temperature range is from 65 °C to 170 °C depending on the amount of reactant (ideal temperature 100 °C - 125 °C). The reaction is carried out in a closed gas-tight vessel (for example a glovebox) that can withstand the pressure that builds up.

Step 1: 2 UO
3 \+ 5 Cl
2 → 2 UCl
5 \+ 3 O

Step 2: 2 UCl
5 \+ Cl
2 → 2 UCl

Overall reaction: 2 UO
3 \+ 6 Cl
2 → 2 UCl
6 \+ 3 O

This metal hexahalide can also be synthesized by blowing Cl
2 gas over sublimed UCl
4 at 350 °C.[8]

Step 1: 2 UCl
4 \+ Cl
2 → 2 UCl

Step 2: 2 UCl
5 \+ Cl
2 → 2 UCl

Overall Reaction: UCl
4 \+ Cl
2 → UCl

## References

1. ↑ Zachariasen, W. H. (1948). "Crystal chemical studies of the 5f-series of elements. V. The crystal structure of uranium hexachloride". Acta Crystallographica 1 (6): 285–287. doi:10.1107/S0365110X48000788.
2. ↑ Taylor, J. C.; Wilson, P. W. (1974). "Neutron and X-ray powder diffraction studies of the structure of uranium hexachloride". Acta Crystallographica Section B 30 (6): 1481. doi:10.1107/S0567740874005115.
3. ↑ Van Dyke, R. E.; Evers, E. C. (1955). "Preparation of Uranium Hexachloride". Google Patents: 2.
4. ↑ Batista, E. R.; Martin, R. L.; Hay, P. J. (2004). "Density Functional Investigations of the Properties and Thermodynamics of UFn and UCln (n=1,...,6)". J. Chem. Phys. 121 (22): 11104–11. doi:10.1063/1.1811607. PMID 15634063. https://zenodo.org/record/1231911.
5. ↑ Lipkin, D.; Wessman, S. (1955). "Process and Apparatus for protecting Uranium hexachloride from Deterioration and Contamination". Google Patents: 2.
6. ↑ 6.0 6.1 6.2 Katz, J.J.; Rabinowitch,E. (1951). The Chemistry of Uranium. Ann Arbor: The McGraw-Hill Book Company.
7. ↑ Van Dyke, R. E.; Evers, E. C. (1955). "Preparation of Uranium Hexachloride". Google Patents: 2.
8. ↑ Thornton, G.; Edelstein, N.; Rösch, N.; Woodwark, D.R.; Edgell, R.G. (1979). "The Electronic Structure of UCl6: Photoelectron Spectra and Scattered Wave Xα Calculations". J. Chem. Phys. 70 (11): 6. doi:10.1063/1.437313. Bibcode: 1979JChPh..70.5218T.

* v
* t
* e

Uranium compounds

U(II)|

* UB2
* US

U(III)|

* UF3
* UCl3
* UI3
* UP
* U(OH)3
* UH3
* UN

| Organouranium(III) compounds|

* U(C5H5)3

|

U(IV)|

* U(BH4)4
* UCl4
* UF4
* UBr4
* UI4
* UO2
* USi2
* US2
* U(SO4)2

| Organouranium(IV) compounds|

* U(C8H8)2
* U(C5H5)4
* U(C5H5)3Cl

|

U(IV,V)|

* U2N3

U(V)|

* UCl5
* UF5
* UBr5
* UI5
* U2O5

U(V,VI)|

* U3O8

U(VI)|

* (NH4)2U2O7
* Na2U2O7
* UCl6
* UF6
* U(PO4)2
* UO3
* UO4
* UO2(CH3COO)2
* UO2(CHO2)2
* UO2CO3
* UO2CO3·2(NH4)2CO3
* UO2Cl2
* UO2F2
* UO2(NO3)2
* UO2(OH)2
* UO2(SO4)2
* ZnUO2(CH3COO)4
* UN2
* H2UO4
* UO6 (hypothetical)

U(XII)|

* UO6 (hypothetical)

* v
* t
* e

Salts and covalent derivatives of the chloride ion

HCl |  |  |  | He

|
|
|
|

LiCl | BeCl2 | BCl3
B2Cl4 | CCl4 | NCl3
ClN3 | Cl2O
ClO2
Cl2O7 | ClF
ClF3
ClF5 | Ne
NaCl | MgCl2 | AlCl
AlCl3 | SiCl4 | P2Cl4
PCl3
PCl5 | S2Cl2
SCl2
SCl4 | Cl2 | Ar
KCl | CaCl
CaCl2 | ScCl3 | TiCl2
TiCl3
TiCl4 | VCl2
VCl3
VCl4
VCl5 | CrCl2
CrCl3
CrCl4 | MnCl2 | FeCl2
FeCl3 | CoCl2
CoCl3 | NiCl2 | CuCl
CuCl2 | ZnCl2 | GaCl2
GaCl3 | GeCl2
GeCl4 | AsCl3
AsCl5 | Se2Cl2
SeCl4 | BrCl | KrCl
RbCl | SrCl2 | YCl3 | ZrCl3
ZrCl4 | NbCl4
NbCl5 | MoCl2
MoCl3
MoCl4
MoCl5
MoCl6 | TcCl4 | RuCl3 | RhCl3 | PdCl2 | AgCl | CdCl2 | InCl
InCl2
InCl3 | SnCl2
SnCl4 | SbCl3
SbCl5 | Te3Cl2
TeCl4 | ICl
ICl3 | XeCl
XeCl2
CsCl | BaCl2 |  | HfCl4 | TaCl5 | WCl2
WCl3
WCl4
WCl5
WCl6 | Re3Cl9
ReCl4
ReCl5
ReCl6 | OsCl4 | IrCl2
IrCl3
IrCl4 | PtCl2
PtCl4 | AuCl
AuCl3 | Hg2Cl2,
HgCl2 | TlCl | PbCl2,
PbCl4 | BiCl3 | PoCl2,
PoCl4 | AtCl  | RnCl2
FrCl | RaCl2 |  | Rf  | Db  | Sg  | Bh  | Hs  | Mt  | Ds  | Rg  | Cn  | Nh  | Fl  | Mc  | Lv  | Ts  | Og
| ↓  |  |
LaCl3 | CeCl3 | PrCl3 | NdCl2,
NdCl3 | PmCl3 | SmCl2,
SmCl3 | EuCl2,
EuCl3 | GdCl3 | TbCl3 | DyCl2,
DyCl3 | HoCl3 | ErCl3 | TmCl2
TmCl3 | YbCl2
YbCl3 | LuCl3
AcCl3 | ThCl4 | PaCl5 | UCl3
UCl4
UCl5
UCl6 | NpCl4 | PuCl3 | AmCl2
AmCl3 | CmCl3 | BkCl3 | CfCl3 | EsCl3 | Fm  | Md  | No  | LrCl3

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