Uranium hexachloride

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), 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 ().

Reaction with hydrogen fluoride

When treated with liquid hydrogen fluoride (HF) at room temperature, produces . :

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 (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 also form upon combining and at 350 °C.{{cite journal|title=The Electronic Structure of UCl6: Photoelectron Spectra and Scattered Wave Xα Calculations|year=1979|last1=Thornton|first1=G.|last2=Edelstein|first2=N.

Step 1:

Step 2:

Overall Reaction:

References

References

1. (1976). "Uranium Hexachloride: (''Hexachlorouranium'' )".
2. (1955). "Preparation of Uranium Hexachloride". Google Patents.
3. (1948). "Crystal Chemical studies of the 5f-series of elements. V. The Crystal structure of Uranium hexachloride". Acta Crystallographica.
4. (1974). "Neutron and X-ray powder diffraction studies of the structure of uranium hexachloride". Acta Crystallographica Section B.
5. (2004). "Density Functional Investigations of the Properties and Thermodynamics of UF_n and UCl_n (n=1,...,6)". J. Chem. Phys..
6. (1951). "The Chemistry of Uranium". The McGraw-Hill Book Company.
7. (1955). "Preparation of Uranium Hexachloride". Google Patents.