Uranium hexachloride

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Uranium hexachloride
Names
IUPAC name
Uranium(VI) chloride
Other names
Uranium hexachloride
Peruranic chloride
Identifiers
3D model ( JSmol )
ChemSpider
  • InChI=1S/6ClH.U/h6*1H;/p-6
    Key: XFCORTPUZRSUIZ-UHFFFAOYSA-H
  • [Cl-].[Cl-].[Cl-].[Cl-].[Cl-].[Cl-].[U]
Properties
UCl 6
Molar mass 450.745 g/mol
Appearance dark green crystalline solid
Density 3.6 g/cm 3
Melting point 177 °C (351 °F; 450 K)
Related compounds
Other anions
Uranium hexafluoride
Other cations
Tungsten hexachloride
Related uranium chlorides
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Uranium hexachloride ( UCl 6 ) is an inorganic chemical compound of uranium in the +6 oxidation state . [1] [2] UCl 6 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] UCl 6 is stable in a vacuum , dry air, nitrogen and helium at room temperature . It is soluble in carbon tetrachloride ( CCl 4 ). Compared to the other uranium halides, little is known about UCl 6 .

Structure and Bonding [ edit ]

Uranium hexachloride has an octahedral geometry, with point group O h . Its lattice (dimensions: 10.95 ± 0.02 A x 6.03 ± 0.01 A) is hexagonal in shape with three molecules per cell; the average theoretical U-Cl bond is 2.472 A long (the experimental U-Cl length found by X-ray diffraction is 2.42 A), [4] and the distance between two adjacent chlorine atoms is 3.65 A.

Chemical properties [ edit ]

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 [ edit ]

UCl 6 is stable up to temperatures between 120 °C and 150 °C. The decomposition of UCl 6 results in a solid phase transition from one crystal form of UCl 6 to another more stable form. [6] However, the decomposition of gaseous UCl 6 produces UCl 5 . The activation energy for this reaction is about 40 kcal per mole .

2 UCl 6 (g) → 2 UCl 5 (s) + Cl 2 (g)

Solubility [ edit ]

UCl 6 is not a very soluble compound. It dissolves in CCl 4 to give a brown solution. It is slightly soluble in isobutyl bromide and in fluorocarbon ( C 7 F 16 ). [6]

Solvents Temperature (°C) Grams of UCl 6 /100g of solution
CCl 4 ?18 2.64
CCl 4 0 4.9
CCl 4 20 7.8
6.6% Cl 2  : 93.4% CCl 4 ?20 2.4
12.5% Cl 2  : 87.5% CCl 4 ?20 2.23
12.5% Cl 2  : 87.5% CCl 4 0 3.98
Liquid Cl 2 ?33 2.20
CH 3 Cl ?24 1.16
Benzene 80 Insoluble
Freon 113 45 1.83

Reaction with hydrogen fluoride [ edit ]

When UCl 6 is reacted with purified anhydrous liquid hydrogen fluoride (HF) at room temperature produces UF 5 . [6]

2 UCl 6 + 10 HF → 2 UF 5 + 10 HCl + Cl 2

Synthesis [ edit ]

Uranium hexachloride can be synthesized from the reaction of uranium trioxide ( UO 3 ) with a mixture of liquid CCl 4 and hot chlorine ( Cl 2 ). The yield can be increased if the reaction carried out in the presence of UCl 5 . [7] The UO 3 is converted to UCl 5 , which in turn reacts with the excess Cl 2 to form UCl 6 . 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: 2 UO 3 + 5 Cl 2 → 2 UCl 5 + 3 O 2

Step 2: 2 UCl 5 + Cl 2 → 2 UCl 6

Overall reaction: 2 UO 3 + 6 Cl 2 → 2 UCl 6 + 3 O 2

This metal hexahalide can also be synthesized by blowing Cl 2 gas over sublimed UCl 4 at 350 °C. [8]

Step 1: 2 UCl 4 + Cl 2 → 2 UCl 5

Step 2: 2 UCl 5 + Cl 2 → 2 UCl 6

Overall Reaction: UCl 4 + Cl 2 → UCl 6

References [ edit ]

  1. ^ 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?287. Bibcode : 1948AcCry...1..285Z . doi : 10.1107/S0365110X48000788 .
  2. ^ 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. Bibcode : 1974AcCrB..30.1481T . doi : 10.1107/S0567740874005115 .
  3. ^ Van Dyke, R. E.; Evers, E. C. (1955). "Preparation of Uranium Hexachloride". Google Patents : 2.
  4. ^ Batista, E. R.; Martin, R. L.; Hay, P. J. (2004). "Density Functional Investigations of the Properties and Thermodynamics of UF n and UCl n (n=1,...,6)" . J. Chem. Phys . 121 (22): 11104?11. doi : 10.1063/1.1811607 . PMID   15634063 .
  5. ^ Lipkin, D.; Wessman, S. (1955). "Process and Apparatus for protecting Uranium hexachloride from Deterioration and Contamination". Google Patents : 2.
  6. ^ a b c Katz, J.J.; Rabinowitch,E. (1951). The Chemistry of Uranium . Ann Arbor: The McGraw-Hill Book Company.
  7. ^ Van Dyke, R. E.; Evers, E. C. (1955). "Preparation of Uranium Hexachloride". Google Patents : 2.
  8. ^ Thornton, G.; Edelstein, N.; Rosch, N.; Woodwark, D.R.; Edgell, R.G. (1979). "The Electronic Structure of UCl 6 : Photoelectron Spectra and Scattered Wave X α Calculations". J. Chem. Phys . 70 (11): 6. Bibcode : 1979JChPh..70.5218T . doi : 10.1063/1.437313 .
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