Potassium octachlorodirhenate

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Potassium octachlorodirhenate
Names
Other names
Dipotassium dirhenium(III) octachloride, potassium octachloridodirhenate(III)
Identifiers
  • 13841-78-6
3D model (JSmol)
  • InChI=1S/8ClH.4K.2Re/h8*1H;;;;;;/q;;;;;;;;4*+1;2*+2/p-8
    Key: YPNLHZRHJGLDAU-UHFFFAOYSA-F
  • [K+].[K+].[K+].[K+].Cl[Re-2](Cl)(Cl)(Cl)$[Re-2](Cl)(Cl)(Cl)Cl
Properties
K2Re2Cl8
Appearance blue solid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Potassium octachlorodirhenate(III) is an inorganic compound with the formula K2Re2Cl8. This dark blue salt is well known as an early example of a compound featuring quadruple bond between its metal centers. Although the compound has no practical value, its characterization was significant in opening a new field of research into complexes with quadruple bonds.[1]

Synthesis and reactions[]

Soviet chemists first reported K2[Re2Cl8] in 1954,[2] but it was not until 1964 that Cotton and Harris characterized the compound as featuring a short Re–Re bond, the first of its kind discovered.[3] The results of this classic study subsequently led to new work into other metals capable of forming metal–metal bonds, such as chromium, molybdenum, tungsten, and technetium.[4][5][6]

A high-yield synthesis of the tetrabutylammonium salt involves treating the perrhenate salt with benzoyl chloride followed by HCl:

2 [(n-C4H9)4N]ReO4 + 8 C6H5COCl → [(n-C4H9)4N]2[Re2Cl8] + organic products
Structure of the anion Re
2Cl2−
8.

Octachlorodirhenate(III) is a precursor to other complexes with multiply-bonded rhenium centers as the quadruple bond is quite stable and is often maintained in . For example, upon treatment with concentrated HBr, the complex forms the analogous anion [Re2Br8]2−, which can easily be converted into other dirhenium species.[7]

Structure and bonding[]

Sample of (NBu4)2Re2Cl8, illustrating the blue-green [Re2Cl8]2- chromophore .

In the [Re2Cl8]2−, the Re–Re bond distance is 2.24 Å, the Re–Re–Cl bond angles are 104°, and the Cl–Re–Cl angles are 87°. The chloride ligands are fully eclipsed. Although this geometry results in repulsive interactions between the chloride ions, this conformation allows for maximum δ–δ overlap between the Re(III) centers, a factor which overrides the unfavorable chloride repulsions. The [Re2Cl8]2− anion has a weak electrophilic character.[8][1] With the configuration, Re(III) is well suited to engage in quadruple bonding. Electrons are allocated to give the configuration σ2π4δ2, resulting in a bond order of 4 between the rhenium centers. The brilliant color of the [Re2Cl8]2− arises from the δ→δ* electronic transition.[7]

References[]

  1. ^ a b Cotton, F. A.; Walton, R. A. (1993). Multiple Bonds Between Metal Atoms. Oxford: Oxford University Press. ISBN 0-19-855649-7.
  2. ^ Лидин Р.А., Андреева Л.Л., Молочко В.А. Константы неорганических веществ.(1954)2:161
  3. ^ Cotton, F. A.; Harris, C. B. (1965). "The Crystal and Molecular Structure of Dipotassium Octachlorodirhenate(III) Dihydrate, K2[Re2Cl8]·2H2O". Inorg. Chem. 4 (3): 330–333. doi:10.1021/ic50025a015.
  4. ^ Hao, S.; Gambarotta, S.; Bensimon, C. (1992). "Reversible cleavage of chromium–chromium quadruple bond of [Me8Cr2][Li(THF)]4 via modification of the coordination sphere of the alkali cation. Preparation and crystal structure of monomeric [Me4Cr][Li(TMEDA)]2". J. Am. Chem. Soc. 114 (9): 3556–3557. doi:10.1021/ja00035a061.
  5. ^ Cotton, F. A.; Eglin, J. L.; Hong, B.; James, C. A. (1992). "Singlet–triplet separations measured by phosphorus-31 nuclear magnetic resonance spectroscopy. Applications to the molybdenum–molybdenum quadruple bond and to edge-sharing bioctahedral complexes". J. Am. Chem. Soc. 114 (12): 4915–4917. doi:10.1021/ja00038a074.
  6. ^ F. A., Cotton; H., Chen; L. M., Daniels; X., Feng (1992). "Partial paramagnetism of the chromium–chromium quadruple bond". J. Am. Chem. Soc. 114 (23): 8980–8983. doi:10.1021/ja00049a031.
  7. ^ a b Barder, T. J.; Walton, R. A. (1985). "Tetrabutylammonium Octachlorodirhenate(III)". Inorg. Synth. 23: 116–118. doi:10.1002/9780470132548.ch22.
  8. ^ Shtemenko, A. V.; Kozhura, O. V.; Pasenko, A. A.; Domasevich, K. V. (2003). "New octachlorodirhenate(III) salts: solid-state manifestation for a certain conformational flexibility of the [Re2Cl8]2− ion". Polyhedron. 22 (12): 4191–4196. doi:10.1016/S0277-5387(03)00288-2.
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