Chalcogenide

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Cadmium sulfide, a prototypical metal chalcogenide, is used as a yellow pigment.

A chalcogenide is a chemical compound consisting of at least one

solid lubricant
.

Alkali metal and alkaline earth chalcogenides

Alkali metal and alkaline earth monochalcogenides are salt-like, being colourless and often water-soluble. The sulfides tend to undergo hydrolysis to form derivatives containing bisulfide (SH−) anions. The alkali metal chalcogenides often crystallize with the antifluorite structure and the alkaline earth salts in the sodium chloride motif.

The zinc blende structure is a common motif for metal monochalcogenides.

Transition metal chalcogenides

Transition metal chalcogenides occur with many stoichiometries and many structures.[2] Most common and most important technologically, however, are the chalcogenides of simple stoichiometries, such as 1:1 and 1:2. Extreme cases include metal-rich phases (e.g. Ta2S), which exhibit extensive metal-metal bonding,[3] and chalcogenide-rich materials such as Re2S7, which features extensive chalcogen-chalcogen bonding.

For the purpose of classifying these materials, the chalcogenide is often viewed as a dianion, i.e.,

covalent, not ionic, as indicated by their semiconducting properties.[2]

Metal-rich chalcogenides

Structure of the metal-rich sulfide Nb21S8.[4]

In most of their chalcogenides, transition metals adopt oxidation states of II or greater. Nonetheless, several examples exist where the metallic atoms far outnumber the chalcogens. Such compounds typically have extensive metal-metal bonding.[5]

Monochalcogenides

Metal monochalcogenides have the formula ME, where M = a transition metal and E = S, Se, Te. They typically crystallize in one of two motifs, named after the corresponding forms of

nonstoichiometry.[6]

Important monochalcogenides include some pigments, notably cadmium sulfide. Many minerals and ores are monosulfides.[1]

Dichalcogenides

MoS2, the most common metal dichalcogenide, adopts a layered structure.

Metal dichalcogenides have the formula ME2, where M = a transition metal and E = S, Se, Te.[7] The most important members are the sulfides. They are always dark diamagnetic solids, insoluble in all solvents, and exhibit semiconducting properties. Some are superconductors.[8]

In terms of their electronic structures, these compounds are usually viewed as derivatives of M4+, where M4+ = Ti4+ (d0 configuration), V4+ (d1 configuration), Mo4+ (d2 configuration).

solid lubricant and catalyst for hydrodesulfurization. The corresponding diselenides and even ditellurides are known, e.g., TiSe2, MoSe2, and WSe2
.

Transition metals

Transition metal dichalcogenides typically adopt either

alkali metals. The intercalation process is accompanied by charge transfer, reducing the M(IV) centers to M(III). The attraction between electrons and holes in 2D tungsten diselenide is 100s of times stronger than in a typical 3D semiconductor.[8]

Pyrite and related disulfides

In contrast to classical metal dichalcogenides,

iron pyrite, a common mineral, is usually described as consisting of Fe2+ and the persulfido anion S22−. The sulfur atoms within the persulfido dianion are bound together via a short S-S bond.[2] "Late" transition metal disulfides (Mn, Fe, Co, Ni) almost always adopt the pyrite or the related marcasite
motif, in contrast to early metals (V, Ti, Mo, W) which adopt 4+ oxidation state with two chalcogenide dianions.

Tri- and tetrachalcogenides

Several metals, mainly for the early metals (Ti, V, Cr, Mn groups) also form trichalcogenides. These materials are usually described as M4+(E22−)(E2−) (where E = S, Se, Te). A well known example is niobium triselenide. Amorphous MoS3 is produced by treatment of tetrathiomolybdate with acid:

MoS42− + 2 H+ → MoS3 + H2S

The mineral patrónite, which has the formula VS4, is an example of a metal tetrachalcogenide. Crystallographic analysis shows that the material can be considered a bis(persulfide), i.e. V4+,(S22−)2.[2]

Main group chalcogenides

As2S3 is a crosslinked polymer where the As and S centers obey the octet rule.

Chalcogen derivatives are known for all of the

S4N4. The structures of many main group materials are dictated by directional covalent bonding, rather than by close packing.[1]

The chalcogen is assigned positive oxidation states for the halides, nitrides, and oxides.

See also

References

  1. ^
    ISBN 0-7506-3365-4
    .
  2. ^
    ISBN 0-521-21489-0
    .
  3. doi:10.1016/0925-8388(95)01688-0
    .
  4. doi:10.1107/S0567740868002463
    .
  5. doi:10.1016/0079-6786(78)90002-X
    .
  6. ISBN 0-939950-01-4
  7. ISBN 0-19-855370-6
    .
  8. ^ a b Wood, Charlie (2022-08-16). "Physics Duo Finds Magic in Two Dimensions". Quanta Magazine. Retrieved 2022-08-22.

External links

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