Pentacyanocobaltate
Identifiers
3D model (JSmol)
  • InChI=1S/5CN.Co/c5*1-2;/q5*-1;+2
    Key: YOZCCRZCYZQCAC-UHFFFAOYSA-N
  • [C-]#N.[C-]#N.[C-]#N.[C-]#N.[C-]#N.[Co+2]
Properties
C5CoN53−
Molar mass 189.025 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

In chemistry, pentacyanocobaltate is the coordination complex with the formula [Co(CN)5]3−. 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.[1] 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]3−.[2]

Reactions

Solutions of [Co(CN)5]3− 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:[1]

2[Co(CN)5]3− + H2 → 2 [Co(CN)5H]3−

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]3− + H2O → [Co(CN)5H]3− + [Co(CN)5OH]3−

In concentrated solution, the complex dimerizes:

2[Co(CN)5]3− → [(NC)5Co−Co(CN)5]6−

With benzyl chloride and related alkylating agents, Co(III) alkyls are formed:[3]

2[Co(CN)5]3− + C6H5CH2Cl → [Co(CN)5CH2C6H5]3− + [Co(CN)5Cl]3−

References

  1. 1 2 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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