Chalcogenide

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

A chalcogenide is a chemical compound consisting of at least one chalcogen anion and at least one more electropositive element. Although all group 16 elements of the periodic table are defined as chalcogens, the term chalcogenide is more commonly reserved for sulfides, selenides, tellurides, and polonides, rather than oxides. [1] Many metal ores exist as chalcogenides. Photoconductive chalcogenide glasses are used in xerography. Some pigments and catalysts are also based on chalcogenides. The metal dichalcogenide MoS2 is a common solid lubricant.

Contents

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. Sphalerite-unit-cell-3D-balls.png
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., S2−, Se2−, Te2−, and Po2−. In fact, transition metal chalcogenides are highly covalent, not ionic, as indicated by their semiconducting properties. [2]

Metal-rich chalcogenides

Structure of the metal-rich sulfide Nb21S8. Nb21S8.png
Structure of the metal-rich sulfide Nb21S8.

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 zinc sulfide. In the zinc blende structure, the sulfide atoms pack in a cubic symmetry and the Zn2+ ions occupy half of the tetrahedral holes. The result is a diamondoid framework. The main alternative structure for the monochalcogenides is the wurtzite structure wherein the atom connectivities are similar (tetrahedral), but the crystal symmetry is hexagonal. A third motif for metal monochalcogenide is the nickel arsenide lattice, where the metal and chalcogenide each have octahedral and trigonal prismatic coordination, respectively. This motif is commonly subject to 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. Molybdenite-3D-balls.png
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). Titanium disulfide was investigated in prototype cathodes for secondary batteries, exploiting its ability to reversibly undergo intercalation by lithium. Molybdenum disulfide is the subject of thousands of articles and the main ore of molybdenum, termed molybdenite. It is used as a 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 cadmium diiodide or molybdenum disulfide structures. In the CdI2 motif, the metals exhibit octahedral structures. In the MoS2 motif, which is not observed for dihalides, the metals exhibit trigonal prismatic structures. [1] The strong bonding between the metal and chalcogenide ligands, contrasts with the weak chalcogenide—chalcogenide bonding between the layers. Owing to these contrasting bond strengths, these materials engage in intercalation by 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]

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. Orpiment-unit-cell-3D.png
As2S3 is a crosslinked polymer where the As and S centers obey the octet rule.

Chalcogen derivatives are known for all of the main group elements except the noble gases. Usually, their stoichiometries follow the classical valence trends, e.g. SiS2, B2S3, Sb2S3. Many exceptions exist however, e.g. P4S3 and 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

Related Research Articles

<span class="mw-page-title-main">Chalcogen</span> Group of chemical elements

The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioactive elements polonium (Po) and livermorium (Lv). Often, oxygen is treated separately from the other chalcogens, sometimes even excluded from the scope of the term "chalcogen" altogether, due to its very different chemical behavior from sulfur, selenium, tellurium, and polonium. The word "chalcogen" is derived from a combination of the Greek word khalkόs (χαλκός) principally meaning copper, and the Latinized Greek word genēs, meaning born or produced.

<span class="mw-page-title-main">Oxide</span> Chemical compound where oxygen atoms are combined with atoms of other elements

An oxide is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– ion with oxygen in the oxidation state of −2. Most of the Earth's crust consists of oxides. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 that protects the foil from further oxidation.

Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. Sulfide also refers to chemical compounds large families of inorganic and organic compounds, e.g. lead sulfide and dimethyl sulfide. Hydrogen sulfide (H2S) and bisulfide (SH−) are the conjugate acids of sulfide.

<span class="mw-page-title-main">Molybdenum disulfide</span> Chemical compound

Molybdenum disulfide is an inorganic compound composed of molybdenum and sulfur. Its chemical formula is MoS
2.

Molybdenum trioxide describes a family of inorganic compounds with the formula MoO3(H2O)n where n = 0, 1, 2. These compounds are produced on the largest scale of any molybdenum compound. The anhydrous oxide is a precursor to molybdenum metal, an important alloying agent. It is also an important industrial catalyst. It is a yellow solid, although impure samples can appear blue or green.

In chemistry, an arsenide is a compound of arsenic with a less electronegative element or elements. Many metals form binary compounds containing arsenic, and these are called arsenides. They exist with many stoichiometries, and in this respect arsenides are similar to phosphides.

Octahedral clusters are inorganic or organometallic cluster compounds composed of six metals in an octahedral array. Many types of compounds are known, but all are synthetic.

<span class="mw-page-title-main">Copper monosulfide</span> Chemical compound

Copper monosulfide is a chemical compound of copper and sulfur. It was initially thought to occur in nature as the dark indigo blue mineral covellite. However, it was later shown to be rather a cuprous compound, formula Cu+3S(S2). CuS is a moderate conductor of electricity. A black colloidal precipitate of CuS is formed when hydrogen sulfide, H2S, is bubbled through solutions of Cu(II) salts. It is one of a number of binary compounds of copper and sulfur (see copper sulfide for an overview of this subject), and has attracted interest because of its potential uses in catalysis and photovoltaics.

<span class="mw-page-title-main">Tungsten disulfide</span> Chemical compound

Tungsten disulfide is an inorganic chemical compound composed of tungsten and sulfur with the chemical formula WS2. This compound is part of the group of materials called the transition metal dichalcogenides. It occurs naturally as the rare mineral tungstenite. This material is a component of certain catalysts used for hydrodesulfurization and hydrodenitrification.

<span class="mw-page-title-main">Tantalum(IV) sulfide</span> Chemical compound

Tantalum(IV) sulfide is an inorganic compound with the formula TaS2. It is a layered compound with three-coordinate sulfide centres and trigonal prismatic or octahedral metal centres. It is structurally similar to molybdenum disulfide MoS2, and numerous other transition metal dichalcogenide materials. The 1T-TaS2 polytype exhibits some unusual properties. In common with many other transition metal dichalcogenide (TMD) compounds, which are metallic at high temperatures, it exhibits a series of charge-density-wave (CDW) phase transitions from 550 K to 50 K. It is unusual amongst them in showing a low-temperature insulating state below 200 K, which is believed to arise from electron correlations, similar to many oxides. The insulating state is commonly attributed to a Mott state. It is also superconducting under pressure or upon doping, with a familiar dome-like phase diagram as a function of dopant, or substituted isovalent element concentration.

<span class="mw-page-title-main">Molybdenum(II) chloride</span> Chemical compound

Molybdenum dichloride describes chemical compounds with the empirical formula MoCl2. At least two forms are known, and both have attracted much attention from academic researchers because of the unexpected structures seen for these compounds and the fact that they give rise to hundreds of derivatives. The form discussed here is Mo6Cl12. The other molybdenum(II) chloride is potassium octachlorodimolybdate.

Copper sulfides describe a family of chemical compounds and minerals with the formula CuxSy. Both minerals and synthetic materials comprise these compounds. Some copper sulfides are economically important ores.

<span class="mw-page-title-main">Titanium disulfide</span> Inorganic chemical compound

Titanium disulfide is an inorganic compound with the formula TiS2. A golden yellow solid with high electrical conductivity, it belongs to a group of compounds called transition metal dichalcogenides, which consist of the stoichiometry ME2. TiS2 has been employed as a cathode material in rechargeable batteries.

<span class="mw-page-title-main">Titanium diselenide</span> Chemical compound

Titanium diselenide (TiSe2) also known as titanium(IV) selenide, is an inorganic compound of titanium and selenium. In this material selenium is viewed as selenide (Se2−) which requires that titanium exists as Ti4+. Titanium diselenide is a member of metal dichalcogenides, compounds that consist of a metal and an element of the chalcogen column within the periodic table. Many exhibit properties of potential value in battery technology, such as intercalation and electrical conductivity, although most applications focus on the less toxic and lighter disulfides, e.g. TiS2.

<span class="mw-page-title-main">Molybdenum diselenide</span> Chemical compound

Molybdenum diselenide is an inorganic compound of molybdenum and selenium. Its structure is similar to that of MoS
2. Compounds of this category are known as transition metal dichalcogenides, abbreviated TMDCs. These compounds, as the name suggests, are made up of a transition metals and elements of group 16 on the periodic table of the elements. Compared to MoS
2, MoSe
2 exhibits higher electrical conductivity.

<span class="mw-page-title-main">Transition metal dichalcogenide monolayers</span> Thin semiconductors

Transition-metal dichalcogenide (TMD or TMDC) monolayers are atomically thin semiconductors of the type MX2, with M a transition-metal atom (Mo, W, etc.) and X a chalcogen atom (S, Se, or Te). One layer of M atoms is sandwiched between two layers of X atoms. They are part of the large family of so-called 2D materials, named so to emphasize their extraordinary thinness. For example, a MoS2 monolayer is only 6.5 Å thick. The key feature of these materials is the interaction of large atoms in the 2D structure as compared with first-row transition-metal dichalcogenides, e.g., WTe2 exhibits anomalous giant magnetoresistance and superconductivity.

<span class="mw-page-title-main">Molybdenum ditelluride</span> Chemical compound

Molybdenum(IV) telluride, molybdenum ditelluride or just molybdenum telluride is a compound of molybdenum and tellurium with formula MoTe2, corresponding to a mass percentage of 27.32% molybdenum and 72.68% tellurium. It can crystallise in two dimensional sheets which can be thinned down to monolayers that are flexible and almost transparent. It is a semiconductor, and can fluoresce. It is part of a class of materials called transition metal dichalcogenides. As a semiconductor the band gap lies in the infrared region. This raises the potential use as a semiconductor in electronics or an infrared detector.

Hydrogen chalcogenides are binary compounds of hydrogen with chalcogen atoms. Water, the first chemical compound in this series, contains one oxygen atom and two hydrogen atoms, and is the most common compound on the Earth's surface.

<span class="mw-page-title-main">Layered materials</span>

In material science, layered materials are solids with highly anisotropic bonding, in which two-dimensional sheets are internally strongly bonded, but only weakly bonded to adjacent layers. Owing to their distinctive structures, layered materials are often suitable for intercalation reactions.

Rhenium compounds are compounds formed by the transition metal rhenium (Re). Rhenium can form in many oxidation states, and compounds are known for every oxidation state from -3 to +7 except -2, although the oxidation states +7, +6, +4, and +2 are the most common. Rhenium is most available commercially as salts of perrhenate, including sodium and ammonium perrhenates. These are white, water-soluble compounds. Tetrathioperrhenate anion [ReS4]− is possible.

References

  1. 1 2 3 4 Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN   0-7506-3365-4.
  2. 1 2 3 4 Vaughan, D. J.; Craig, J. R. "Mineral Chemistry of Metal Sulfides" Cambridge University Press, Cambridge: 1978. ISBN   0-521-21489-0.
  3. ↑ Hughbanks, Timothy (1995). "Exploring the metal-rich chemistry of the early transition elements". Journal of Alloys and Compounds. 229: 40–53. doi:10.1016/0925-8388(95)01688-0.
  4. ↑ Franzen, H.F.; Beineke, T.A.; Conrad, B.R. (1968). "The crystal structure of Nb21S8". Acta Crystallographica B. 24 (3): 412–p416. doi:10.1107/S0567740868002463.
  5. ↑ Franzen, Hugo F. (1978). "Structure and Bonding of Metal-Rich Compounds: Pnictides, chalcogenides and halides". Progress in Solid State Chemistry. 12: 1–39. doi:10.1016/0079-6786(78)90002-X.
  6. ↑ "Sulfide Mineralogy: Volume 1" Paul H. Ribbe, editor, 1974, Mineralogical Society of America. ISBN   0-939950-01-4
  7. ↑ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN   0-19-855370-6.
  8. 1 2 Wood, Charlie (2022-08-16). "Physics Duo Finds Magic in Two Dimensions". Quanta Magazine. Retrieved 2022-08-22.
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