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Pentacyanocobaltate

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Pentacyanocobaltate
Identifiers
CAS Number
3D model (JSmol)
PubChem CID
InChI
  • InChI=1S/5CN.Co/c5*1-2;/q5*-1;+2Key: YOZCCRZCYZQCAC-UHFFFAOYSA-N
SMILES
  • #C(C#)(C#)(C#)C#
Properties
Chemical formula C5CoN5
Molar mass 189.025 g·mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Infobox references
Chemical compound

In chemistry, pentacyanocobaltate is the coordination complex with the formula [Co(CN)5]. When crystallized with a quaternary ammonium cation, it can be obtained as a yellow solid. Pentacyanocobaltate attracted attention as an early example of a metal complex that reacts with hydrogen. It contains low-spin cobalt(II), with a doublet ground state.

Synthesis and structure

Aqueous solutions of pentacyanocobaltate are produced by the addition of five or more equivalents of a cyanide salt to a solution of a cobalt(II) salt. Initially this reaction produces insoluble cobalt dicyanide, but this solid dissolves in the presence of the excess cyanide. Pentacyanocobaltate forms within seconds. When prepared using a quaternary ammonium (quat) cyanide, crystals can be obtained with the formula (quat)3[Co(CN)5]. According to X-ray crystallography, the salt features square pyamidal [Co(CN)5].

Reactions

Solutions of [Co(CN)5] undergo a variety of reactions. The complex attracted attention in the 1940s for its reactivity toward hydrogen, which is now understood to produce a cobalt hydride:

2[Co(CN)5] + H2 → 2 [Co(CN)5H]

When allowed to stand as a dilute solution for several minutes, the complex reacts with water to give two Co(III) derivatives:

2[Co(CN)5] + H2O → [Co(CN)5H] + [Co(CN)5OH]

In concentrated solution, the complex dimerizes:

2[Co(CN)5] → [(NC)5Co−Co(CN)5]

With benzyl chloride and related alkylating agents, Co(III) alkyls are formed:

2[Co(CN)5] + C6H5CH2Cl → [Co(CN)5CH2C6H5] + [Co(CN)5Cl]

References

  1. ^ Kwiatek, Jack (1968). "Reactions Catalyzed by Pentacyanocobaltate(II)". Catalysis Reviews. 1: 37–72. doi:10.1080/01614946808064700.
  2. Brown, Leo D.; Raymond, Kenneth N. (1975). "Structural Characterization of the Pentacyanocobaltate(II) Anion in the Salt Tris(diethyldiisopropylammonium) Pentacyanocobaltate(II)". Inorganic Chemistry. 14 (11): 2590–2594. doi:10.1021/ic50153a002.
  3. Chock, Pwen Boon; Halpern, Jack (1969). "Reactions of Pentacyanocobaltate(II) with Some Organic Halides". Journal of the American Chemical Society. 91 (3): 582–588. doi:10.1021/ja01031a010.
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