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In chemistry, a polyselenide usually refers to anions of the formula (Sen)2-, where Se is the atomic symbol for the element
Polyselenides are prone to decomposition on exposure to air, in which case they are oxidized back to elemental selenium.
: + 2 H+ + O2 → ''n'' Se + H2O
As ligands in
In chemistry, a polyselenide usually refers to anions of the formula (Sen)2-, where Se is the atomic symbol for the element selenium
Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and telluriu ...
. Many main group and transition metal
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that c ...
s form complexes with polyselenide anions.
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. These reactions appear to proceed by initial formatiion of the alkali metal selenide, followed by the reaction of the latter with additional selenium: :2 Na + Se → Na2Se :Na2Se + ''n'' Se → Na2Se''n''+1 Once generated, alkali metal polyselenides can be converted to lipophilic salts by treatmentcryptand
In chemistry, cryptands are a family of synthetic, bicyclic and polycyclic, multidentate ligands for a variety of cations. The Nobel Prize for Chemistry in 1987 was given to Donald J. Cram, Jean-Marie Lehn, and Charles J. Pedersen for th ...
ligands or by ion exchange with quat salts.Kolis, J. "Coordination Chemistry of Polychalcogen Anions and Transition Metal Carbonyls" Coordination Chemistry Reviews 1990, volume 105, pp. 195-219.
: Na2Se''n'' + 2 R4NCl → (R4N)2Se''n'' + 2 NaCl
Structures
Salts of polyselenides have often been characterized byX-ray crystallography
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angle ...
. 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 Me4sub>2Se6 show three selenium sites. Single-crystal X-ray structure determination of the two salts support the NMR data.
Reactivity
Polyselenides are prone to decomposition on exposure to air, in which case they are oxidized back to elemental selenium.
: + 2 H+ + O2 → ''n'' Se + H2O
As ligands in coordination complex
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...
s, polyselenides are generally bidentate. Complexes of penta-, tetra-, and triselenide ligands are known. One example is the spirocyclic n(Se4)2sup>2-.
Further reading
* *See also
*Polytelluride
In chemistry
Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, mole ...
References