Polyselenides and polytellurides

   Although Se and Te analogues of polysulfanes do not extend beyond the poorly characterized H₂Se₂ and H₂Te₂, the chemistries of polyselenides, polytellurides and their metal complexes are well established. Equations 15.43–1.3 illustrate preparations of salts of [Se_x]^2- and [Te_x]^2- ; for details of crown ethers and cryptands.

                                                 (1.1)

                 (1.2)

           (1.3)

    (1.4)

(1.1)                      (1.1)

  Structurally, the smaller polyselenide and polytelluride ions resemble their polysulfide analogues, e.g. [Te₅]^2- has structure 1.1 with a helically twisted chain. The structures of higher anions are less simple, e.g. [Te₈]^2- (1.1) can be considered in terms of  [Te₄]^2- and [Te₃]^2- ligands bound to a Te²⁺ centre. Similarly, [Se₁₁]^2- can be described in terms of two [Se₅]^2- ligands chelating to an Se²⁺centre. The coordination chemistry of the [Se_x]^2- and [Te_x]^2- chain anions has developed significantly since 1990; examples include [(Te₄)Cu(µ-Te₄)Cu)Te₄(]^4- and [(Se₄)₂In(µ-Se₅)In(Se₄)₂]^4- (both of which have bridging and chelating ligands), octahedral [Pt(Se₄)₃]^2- with chelating [Se₄]^2- ligands, [Zn(Te₃)(Te₄)]^2- and [Cr(Te₄)₃]^3-.

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