Uranium hexachloride
 | |
| Names | |
|---|---|
| IUPAC name
Uranium(VI) chloride | |
| Other names
Uranium hexachloride Peruranic chloride | |
| Identifiers | |
| Properties | |
| UCl6 | |
| Molar mass | 450.745 g/mol |
| Appearance | dark green crystalline solid |
| Density | 3600 kg/m3 |
| Melting point | 177 °C (351 °F; 450 K) |
| Boiling point | 75 °C (167 °F; 348 K) |
| Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
| Infobox references | |
Uranium hexachloride is an inorganic chemical compound of uranium in the +6 oxidation state.[1][2] The chemical compound Uranium hexachloride (UCl6) 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 373.15K[3] UCl6 is stable in a vacuum, dry air, nitrogen and helium at room temperature. It is soluble in carbon tetrachloride (CCl4). Compared to the other uranium halides, little is known about UCl6.
Structure and Bonding
Uranium hexachloride has an octahedral geometry with a point group of Oh. Its lattice (dimensions: 10.95 ± 0.02Å x 6.03 ± 0.01Å) is hexagon in shape with three molecules per cell; the average theoretical U-Cl bond is 2.472Å long (X-ray diffraction experimental U-Cl length is 2.42Å)[4] and the distance between two adjacent chlorine atoms is 3.65Å .
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
UCl6 is stable up to temperatures between 120oC and 150oC. The decomposition of UCl6 results in a solid phase transition from one crystal form of UCl6 to another more stable form.[6] However the decomposition of gaseous UCl6 produces (UCl5). The Activation energy for this reaction is about 40kcal per mole.
2UCl6 (g) → 2UCl5 (s) + Cl2 (g)
Solubility
UCl6 is not a very soluble compound. It dissolves in CCl4 to give a brown solution. It is slightly soluble in isobutyl bromide and in fluorocarbon (C7F16).[7]
| Solvents | Temperature (oC) | Grams of UCl6/100g of solution |
|---|---|---|
| CCl4 | ||
| 2.64 | ||
| CCl4 | 0 | 4.9 |
| CCl4 | 20 | 7.8 |
| 6.6% Cl2 : 93.4% CCl4 | ||
| 2.4 | ||
| 12.5% Cl2 : 87.5% CCl4 | ||
| 2.23 | ||
| 12.5% Cl2 : 87.5% CCl4 | 0 | 3.98 |
| Liquid Cl2 | ||
| 2.20 | ||
| CH3Cl | ||
| 1.16 | ||
| Benzene | 80 | Insoluble |
| Freon 113 | 45 | 1.83 |
Reaction with Hydrogen Fluoride
When UCl6 is reacted with purified anhydrous liquid Hydrogen Fluoride (HF) at room temperature produces UF5.[8]
2UCl6+ 10HF → 2UF5 + 10HCl + Cl2
Synthesis
Uranium hexachloride can be synthesized from the reaction of uranium trioxide (UO3) with a mixture of liquid CCl4 and hot chlorine (Cl2). However the yield can be increased if the reaction carried out in the presence of UCl5.[9] The UO3 is converted to UCl5, which in turn reacts with the excess Cl2 to form UCl6. It requires a substantial amount of heat for the reaction to take place; the temperature range is from 65oC to 170oC depending on the amount of reactants (ideal temp: 100oC - 125oC) 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: 2UO3 + 5Cl2 → 2UCl5 + 3O2
Step 2: 2UCl5 + Cl2 → 2UCl6
Overall reaction: 2UO3 + 6Cl2 → 2UCl6 + 3O2
This metal hexahalide can also be synthesized by blowing Cl2 gas over sublimed UCl4 at 350oC.[10]
Step 1: 2UCl4 + Cl2 → 2UCl5
Step 2: 2UCl5 + Cl2 → 2UCl6
Overall Reaction: UCl4 + Cl2 → UCl6
References
- ↑ 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. doi:10.1107/S0365110X48000788.
- ↑ 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.
- ↑ Van Dyke, R. E.; Evers, E. C. (1955). "Preparation of Uranium Hexachloride". google patent: 2.
- ↑ 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): 8. doi:10.1063/1.1811607.
- ↑ Lipkin, D.; Wessman, S. (1955). "Process and Apparatus for protecting Uranium hexachloride from Deterioration and Contamination". google patent: 2.
- ↑ Katz,J.J; Rabinowitch,E. (1951). The Chemistry of Uranium. Ann Arbor: The McGraw-Hill Book Company.
- ↑ Katz,J.J; Rabinowitch,E. (1951). The Chemistry of Uranium. Ann Arbor: The McGraw-Hill Book Company.
- ↑ Katz,J.J; Rabinowitch,E. (1951). The Chemistry of Uranium. Ann Arbor: The McGraw-Hill Book Company.
- ↑ Van Dyke, R. E.; Evers, E. C. (1955). "Preparation of Uranium Hexachloride". google patent: 2.
- ↑ 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.