Potassium octachlorodirhenate

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

Potassium octachlorodirhenate(III) is an inorganic compound with the formula K2 Re2 Cl8. 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]

Contents

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] [4] 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. [5] [6] [7]

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 2Cl 8. Octachlorodirhenate(III)-3D-balls.png
Structure of the anion Re
2Cl
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 ligand substitution reactions. For example, upon treatment with concentrated HBr, the complex forms the analogous anion [Re2Br8]2−, which can easily be converted into other dirhenium species. [8]

Structure and bonding

Sample of (NBu4)2Re2Cl8, illustrating the blue-green [Re2Cl8] chromophore . (NBu4)2Re2Cl8.jpg
Sample of (NBu4)2Re2Cl8, illustrating the blue-green [Re2Cl8] 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. [9] [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. [8]

Related Research Articles

<span class="mw-page-title-main">Group 7 element</span> Group of chemical elements

Group 7, numbered by IUPAC nomenclature, is a group of elements in the periodic table. It contains manganese (Mn), technetium (Tc), rhenium (Re) and bohrium (Bh). This group lies in the d-block of the periodic table, and are hence transition metals. This group is sometimes called the manganese group or manganese family after its lightest member; however, the group itself has not acquired a trivial name because it belongs to the broader grouping of the transition metals.

<span class="mw-page-title-main">Chromium(III) chloride</span> Chemical compound

Chromium(III) chloride (also called chromic chloride) is an inorganic chemical compound with the chemical formula CrCl3. It forms several hydrates with the formula CrCl3·nH2O, among which are hydrates where n can be 5 (chromium(III) chloride pentahydrate CrCl3·5H2O) or 6 (chromium(III) chloride hexahydrate CrCl3·6H2O). The anhydrous compound with the formula CrCl3 are violet crystals, while the most common form of the chromium(III) chloride are the dark green crystals of hexahydrate, CrCl3·6H2O. Chromium chlorides find use as catalysts and as precursors to dyes for wool.

<span class="mw-page-title-main">Delta bond</span> Type of Chemical Bond

In chemistry, delta bonds are covalent chemical bonds, where four lobes of one involved atomic orbital overlap four lobes of the other involved atomic orbital. This overlap leads to the formation of a bonding molecular orbital with two nodal planes which contain the internuclear axis and go through both atoms.

<span class="mw-page-title-main">Gold(III) chloride</span> Chemical compound

Gold(III) chloride, traditionally called auric chloride, is an inorganic compound of gold and chlorine with the molecular formula Au2Cl6. The "III" in the name indicates that the gold has an oxidation state of +3, typical for many gold compounds. It has two forms, the monohydrate (AuCl3·H2O) and the anhydrous form, which are both hygroscopic and light-sensitive solids. This compound is a dimer of AuCl3. This compound has a few uses, such as an oxidizing agent and for catalyzing various organic reactions.

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<span class="mw-page-title-main">Quadruple bond</span> Chemical bond involving eight electrons; has one sigma, two pi, and one delta bond

A quadruple bond is a type of chemical bond between two atoms involving eight electrons. This bond is an extension of the more familiar types double bonds and triple bonds. Stable quadruple bonds are most common among the transition metals in the middle of the d-block, such as rhenium, tungsten, technetium, molybdenum and chromium. Typically the ligands that support quadruple bonds are π-donors, not π-acceptors.

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<span class="mw-page-title-main">Potassium octachlorodimolybdate</span> Chemical compound

Potassium octachlorodimolybdate is an inorganic compound with the chemical formula K4[Mo2Cl8]. It is known as a red-coloured, microcrystalline solid. The anion is of historic interest as one of the earliest illustrations of a quadruple bonding. The salt is usually obtained as the pink-coloured dihydrate.

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4, or a compound containing this ion. The perrhenate anion is tetrahedral, being similar in size and shape to perchlorate and the valence isoelectronic permanganate. The perrhenate anion is stable over a broad pH range and can be precipitated from solutions with the use of organic cations. At normal pH, perrhenate exists as metaperrhenate, but at high pH mesoperrhenate forms. Perrhenate, like its conjugate acid perrhenic acid, features rhenium in the oxidation state of +7 with a d0 configuration. Solid perrhenate salts takes on the color of the cation.

<span class="mw-page-title-main">Molybdenum(II) acetate</span> Chemical compound

Molybdenum(II) acetate is a coordination compound with the formula Mo2(O2CCH3)4. It is a yellow, diamagnetic, air-stable solid that is slightly soluble in organic solvents. Molybdenum(II) acetate is an iconic example of a compound with a metal-metal quadruple bond.

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<span class="mw-page-title-main">Molybdate</span> Chemical compound of the form –O–MoO₂–O–

In chemistry, a molybdate is a compound containing an oxyanion with molybdenum in its highest oxidation state of 6: O−−Mo(=O)2−O−. Molybdenum can form a very large range of such oxyanions, which can be discrete structures or polymeric extended structures, although the latter are only found in the solid state. The larger oxyanions are members of group of compounds termed polyoxometalates, and because they contain only one type of metal atom are often called isopolymetalates. The discrete molybdenum oxyanions range in size from the simplest MoO2−
4, found in potassium molybdate up to extremely large structures found in isopoly-molybdenum blues that contain for example 154 Mo atoms. The behaviour of molybdenum is different from the other elements in group 6. Chromium only forms the chromates, CrO2−
4, Cr
2O2−
7, Cr
3O2−
10 and Cr
4O2−
13 ions which are all based on tetrahedral chromium. Tungsten is similar to molybdenum and forms many tungstates containing 6 coordinate tungsten.

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<span class="mw-page-title-main">Metal–metal bond</span>

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References

  1. 1 2 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. ↑ Cotton, F. A. (March 1965). "Metal-Metal Bonding in [Re 2 X 8 ] 2- Ions and Other Metal Atom Clusters". Inorganic Chemistry. 4 (3): 334–336. doi:10.1021/ic50025a016. ISSN   0020-1669.
  5. ↑ 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.
  6. ↑ 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.
  7. ↑ 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.
  8. 1 2 Barder, T. J.; Walton, R. A. (1985). "Tetrabutylammonium Octachlorodirhenate(III)". Inorganic Syntheses. pp. 116–118. doi:10.1002/9780470132548.ch22. ISBN   9780470132548.{{cite book}}: |journal= ignored (help)
  9. ↑ 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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