Polyselenide

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Structures of two polyselenide anions.

In

main group and transition metals form complexes with polyselenide anions.[1]

Preparation

Conceptually, polyselenides are derived by deprotonation polyselenanes H2Sen, but such species are rare or unstable. Instead, analogous to the preparation of many

Zintl ions, polyselenides are produced by reduction of elemental Se with alkali metals. Such reactions can be conducted by heating a mixture of the solids or by dissolving Se metal in amine solutions of alkali metals. Synthesis can also be conducted in high-boiling, polar, aprotic solvents such as DMF, HMPA, and NMP.[2]
These reactions appear to proceed by initial formation of the alkali metal selenide, followed by the reaction of the latter with additional selenium:

2 Na + Se → Na2Se
Na2Se + n Se → Na2Sen+1

Once generated, alkali metal polyselenides can be converted to lipophilic salts by treatment

quat salts.[3]

Na2Sen + 2 R4NCl → (R4N)2Sen + 2 NaCl

Structures

Salts of polyselenides have often been characterized by X-ray crystallography. Polyselenides salts generally feature open chains, which adopt a zig-zag conformation. In rare cases, cyclic structures are observed as in Li2Se5, which features a square-planar Se center. High resolution solid state 77Se NMR spectra of [NMe4]2Se6 show three selenium sites. Single-crystal X-ray structure determination of the two salts support the NMR data.[4]

Reactivity

Structure of (C5H5)2TiSe5.

Polyselenides are prone to decomposition on exposure to air, in which case they are oxidized back to elemental selenium.

Se2−
n + 2 H+ + 1⁄2 O2 → n Se + H2O

As ligands in coordination complexs, polyselenides are generally bidentate. Complexes of penta-, tetra-, and triselenide ligands are known. One example is the spirocyclic [Zn(Se4)2]2-.[5]

Further reading

  • Graf, Christian; Assoud, Abdeljalil; Mayasree, Oottil; Kleinke, Holger (2009). "Solid State Polyselenides and Polytellurides: A Large Variety of Se–Se and Te–Te Interactions". Molecules. 14 (9): 3115–3131.
    PMID 19783911
    .
  • Sheldrick, William S. (2012). "Polychalcogenide Anions: Structural Diversity and Ligand Versatility". Zeitschrift für Anorganische und Allgemeine Chemie. 638 (15): 2401–2424.
    doi:10.1002/zaac.201200241
    .

See also

References

  1. ISBN 978-0-08-037941-8
    .
  2. doi:10.1021/jo00244a051
    .
  3. doi:10.1016/0010-8545(90)80023-M
  4. ^ Barrie, P. J.; Clark, R. J. H.; Selenium Solid-State NMR Spectroscopy and Structures of Tetramethylammonium Pentaselenide and Hexaselenide Complexes. Inorg. Chem, 1995, 34, 4299–4304 DOI: 10.1021/ic00121a006
  5. doi:10.1080/02603599008048650
    .
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