Uranium hexachloride
Uranium hexachloride is the inorganic compound with the formula. It features uranium in the +6 oxidation state. hydrolyzes readily but is stable under inert atmosphere. It is soluble in carbon tetrachloride. It is a multi-luminescent dark green or black solid with a vapor pressure between 1-3 mmHg at 373.15 K.
Structure and bonding
Uranium hexachloride has an octahedral geometry, with point group Oh. Its lattice is hexagonal in shape with three molecules per cell; the average theoretical U-Cl bond is 2.472 Å long, and the distance between two adjacent chlorine atoms is 3.65 Å.Chemical properties
is stable up to temperatures between 120 °C and 150 °C. The decomposition of results in a solid phase transition from one crystal form of to another more stable form. It decomposes as follows:The activation energy for this reaction is about 40 kcal per mole.
Solubility
is not a very soluble compound. It dissolves in to give a brown solution. It is slightly soluble in isobutyl bromide and in fluorocarbon.| Solvents | Temperature | Grams of /100g of solution |
| [Carbon tetrachloride|] | −18 | 2.64 |
| [Carbon tetrachloride|] | 0 | 4.9 |
| [Carbon tetrachloride|] | 20 | 7.8 |
| 6.6% [Chlorine|] : 93.4% [Carbon tetrachloride|] | −20 | 2.4 |
| 12.5% [Chlorine|] : 87.5% [Carbon tetrachloride|] | −20 | 2.23 |
| 12.5% [Chlorine|] : 87.5% [Carbon tetrachloride|] | 0 | 3.98 |
| Liquid [Chlorine|] | −33 | 2.20 |
| [Chloromethane|] | −24 | 1.16 |
| Benzene | 80 | Insoluble |
| Freon 113 | 45 | 1.83 |
Reaction with hydrogen fluoride
When treated with liquid hydrogen fluoride at room temperature, produces [uranium pentafluoride|].Synthesis
Uranium hexachloride is efficiently prepared from uranium hexafluoride by halide exchange using boron trichloride according to the following idealized equation:Uranium hexachloride can also be synthesized from the reaction of uranium trioxide with a mixture of liquid and hot chlorine. The yield can be increased if the reaction carried out in the presence of. The is converted to, which in turn reacts with the excess to form. 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. The reaction is carried out in a closed gas-tight vessel that can withstand the pressure that builds up.
Step 1:
Step 2:
Overall reaction:
This metal hexahalide also form upon combining and at 350 °C.
Step 1:
Step 2:
Overall Reaction: