Uranium hexachloride is an inorganic chemical compound of uranium in the +6 oxidation state.[1] [2] 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] is stable in a vacuum, dry air, nitrogen and helium at room temperature. It is soluble in carbon tetrachloride . Compared to the other uranium halides, little is known about .
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.
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.
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.[6] However, the decomposition of gaseous produces . The activation energy for this reaction is about 40 kcal per mole.
is not a very soluble compound. It dissolves in to give a brown solution. It is slightly soluble in isobutyl bromide and in fluorocarbon .[6]
| Solvents | Temperature (°C) | Grams of /100g of solution | |
|---|---|---|---|
| −18 | 2.64 | ||
| 0 | 4.9 | ||
| 20 | 7.8 | ||
| −20 | 2.4 | ||
| −20 | 2.23 | ||
| 0 | 3.98 | ||
| −33 | 2.20 | ||
| −24 | 1.16 | ||
| 80 | Insoluble | ||
| 45 | 1.83 |
When is reacted with purified anhydrous liquid hydrogen fluoride (HF) at room temperature produces .[6]
Uranium hexachloride can 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 .[7] 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 (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:
Step 2:
Overall reaction:
This metal hexahalide can also be synthesized by blowing gas over sublimed at 350 °C.[8]
Step 1:
Step 2:
Overall Reaction: