:Uranium hexachloride

Uranium hexachloride has an octahedral geometry, with point group O_h.{{cite journal|doi=10.1107/S0365110X48000788|title=Crystal Chemical studies of the 5f-series of elements. V. The Crystal structure of Uranium hexachloride|year=1948|last1=Zachariasen|first1=W. H.|journal=Acta Crystallographica|volume=1|issue=6|pages=285–287|doi-access=free|bibcode=1948AcCry...1..285Z }}{{cite journal|doi=10.1107/S0567740874005115|title=Neutron and X-ray powder diffraction studies of the structure of uranium hexachloride|year=1974|last1=Taylor|first1=J. C.|last2=Wilson|first2=P. W.|journal=Acta Crystallographica Section B|volume=30|issue=6|pages=1481|bibcode=1974AcCrB..30.1481T }} 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),{{cite journal|doi=10.1063/1.1811607|pmid = 15634063|title=Density Functional Investigations of the Properties and Thermodynamics of UF_n and UCl_n (n=1,...,6)|year=2004|last1=Batista|first1=E. R.|last2=Martin|first2=R. L.|last3=Hay|first3=P. J.|journal=J. Chem. Phys. |volume=121|issue=22|pages=11104–11|url=https://zenodo.org/record/1231911}} and the distance between two adjacent chlorine atoms is 3.65 Å.

{{chem2|UCl6}} is stable up to temperatures between 120 °C and 150 °C. The decomposition of {{chem2|UCl6}} results in a solid phase transition from one crystal form of {{chem2|UCl6}} to another more stable form.{{cite book|author1=Katz|first=J.J.|title=The Chemistry of Uranium|author2=Rabinowitch, E.|publisher=The McGraw-Hill Book Company|year=1951|place=Ann Arbor}} It decomposes as follows:

:{{chem2|2 UCl6 (g) → 2 UCl5 (s) + Cl2 (g)}}

The activation energy for this reaction is about 40 kcal per mole.

{{chem2|UCl6}} is not a very soluble compound. It dissolves in {{chem2|CCl4}} to give a brown solution. It is slightly soluble in isobutyl bromide and in fluorocarbon ({{chem2|C7F16}}).

When treated with liquid hydrogen fluoride (HF) at room temperature, {{chem2|UCl6}} produces uranium pentafluoride.

:{{chem2|2 UCl6 + 10 HF → 2 UF5 + 10 HCl + Cl2}}

Uranium hexachloride is efficiently prepared from uranium hexafluoride by halide exchange using boron trichloride according to the following idealized equation:

:{{chem2| UF6 + 2 BCl3 → UCl6 + 2 BF3}}

Uranium hexachloride can also be synthesized from the reaction of uranium trioxide ({{chem2|UO3}}) with a mixture of liquid {{chem2|CCl4}} and hot chlorine ({{chem2|Cl2}}). The yield can be increased if the reaction carried out in the presence of {{chem2|UCl5}}.{{cite journal|title=Preparation of Uranium Hexachloride|year=1955|last1=Van Dyke|first1=R. E.|last2=Evers|first2=E. C.|journal=Google Patents|pages=2}} The {{chem2|UO3}} is converted to {{chem2|UCl5}}, which in turn reacts with the excess {{chem2|Cl2}} to form {{chem2|UCl6}}. 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: {{chem2|2 UO3 + 5 Cl2 → 2 UCl5 + 3 O2}}

Step 2: {{chem2|2 UCl5 + Cl2 → 2 UCl6}}

Overall reaction: {{chem2|2 UO3 + 6 Cl2 → 2 UCl6 + 3 O2}}

This metal hexahalide also form upon combining {{chem2|Cl2}} and {{chem2|UCl4}} at 350 °C.{{cite journal|title=The Electronic Structure of UCl₆: Photoelectron Spectra and Scattered Wave X_α Calculations|year=1979|last1=Thornton|first1=G.|last2=Edelstein|first2=N.

| last3=Rösch|first3=N.|last4=Woodwark|first4=D.R.

| last5=Edgell|first5=R.G.|journal=J. Chem. Phys. |volume=70|issue=11|pages=6|doi=10.1063/1.437313|bibcode=1979JChPh..70.5218T}}

Step 1: {{chem2|2 UCl4 + Cl2 → 2 UCl5}}

Step 2: {{chem2|2 UCl5 + Cl2 → 2 UCl6}}

Overall Reaction: {{chem2|UCl4 + Cl2 → UCl6}}

{{reflist}}

{{Uranium compounds}}

{{Chlorides}}

{{Actinide halides}}

Category:Uranium(VI) compounds

Category:Chlorides

Category:Actinide halides