:
220px, Cadmium sulfide, a prototypical metal chalcogenide, is used as a yellow pigment.
A chalcogenide is a chemical compound consisting of at least one
chalcogen
The chalcogens (ore forming) ( ) 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 radioact ...
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
and at least one more
electropositive
Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the d ...
element. Although all
group 16 element
The chalcogens (ore forming) ( ) 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 radioact ...
s of the periodic table are defined as chalcogens, the term chalcogenide is more commonly reserved for
sulfide
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 lar ...
s,
selenide A selenide is a chemical compound containing a selenium anion with oxidation number of −2 (Se2−), much as sulfur does in a sulfide. The chemistry of the selenides and sulfides is similar. Similar to sulfide, in aqueous solution, the selenide ion ...
s,
tellurides, and
polonide
A polonide is a chemical compound of the radioactive element polonium with any element less electronegative than polonium. Polonides are usually prepared by a direct reaction between the elements at temperatures of around 300–400 °C... They a ...
s, rather than
oxide
An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...
s.
[ Many metal ores exist as chalcogenides. ]Photoconductive
Photoconductivity is an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation.
Whe ...
chalcogenide glass
Chalcogenide glass (pronounced hard ''ch'' as in ''chemistry'') is a glass containing one or more chalcogens (sulfur, selenium and tellurium, but excluding oxygen). Such glasses are covalently bonded materials and may be classified as covalent netw ...
es are used in xerography
Xerography is a dry photocopying technique. Originally called electrophotography, it was renamed xerography—from the roots el, ξηρός, label=none ''xeros'', meaning "dry" and -γραφία ''-graphia'', meaning "writing"—to emphasize ...
. Some pigments and catalysts are also based on chalcogenides. The metal dichalcogenide MoS2 is a common solid lubricant
Dry lubricants or solid lubricants are materials that, despite being in the solid phase, are able to reduce friction between two surfaces sliding against each other without the need for a liquid oil medium.
The two main dry lubricants are graphit ...
.
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
Bisulfide (or bisulphide in British English) is an inorganic anion with the chemical formula HS− (also written as SH−). It contributes no color to bisulfide salts, and its salts may have a distinctive putrid smell. It is a strong base. Bisul ...
(SH−) anions. The alkali metal chalcogenides often crystallize with the antifluorite
Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon.
The Mohs sca ...
structure and the alkaline earth salts in the sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
motif.
:
Transition metal chalcogenides
Transition metal chalcogenides occur with many stoichiometries and many structures.[Vaughan, D. J.; Craig, J. R. “Mineral Chemistry of Metal Sulfides" Cambridge University Press, Cambridge: 1978. .] 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, 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
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...
, not ionic, as indicated by their semiconducting properties.[
]
Metal-rich chalcogenides
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.
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
Zinc sulfide (or zinc sulphide) is an inorganic compound with the chemical formula of ZnS. This is the main form of zinc found in nature, where it mainly occurs as the mineral sphalerite. Although this mineral is usually black because of various i ...
. In the zinc blende
Sphalerite (sometimes spelled sphaelerite) is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in sedimentary exhalative, Mississippi-Va ...
structure, the sulfide atoms pack in a cubic symmetry and the Zn2+ ions occupy half of the tetrahedral holes. The result is a diamondoid In chemistry, diamondoids are variants of the carbon cage molecule known as adamantane (C10H16), the smallest unit cage structure of the diamond crystal lattice. Diamondoids also known as nanodiamonds or condensed adamantanes may include one or more ...
framework. The main alternative structure for the monochalcogenides is the wurtzite
Wurtzite is a zinc and iron sulfide mineral with the chemical formula , a less frequently encountered Polymorphism (materials science), structural polymorph form of sphalerite. The iron content is variable up to eight percent.Palache, Charles, Har ...
structure wherein the atom connectivities are similar (tetrahedral), but the crystal symmetry is hexagonal. A third motif for metal monochalcogenide is the nickel arsenide
Nickeline or niccolite is a mineral consisting primarily of nickel arsenide (NiAs). The naturally-occurring mineral contains roughly 43.9% nickel and 56.1% arsenic by mass, but composition of the mineral may vary slightly.
Small quantities of ...
lattice, where the metal and chalcogenide each have octahedral and trigonal prismatic coordination, respectively. This motif is commonly subject to nonstoichiometry
In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); m ...
.
Important monochalcogenides include some pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...
s, notably cadmium sulfide
Cadmium sulfide is the inorganic compound with the formula CdS. Cadmium sulfide is a yellow solid.Egon Wiberg, Arnold Frederick Holleman (2001''Inorganic Chemistry'' Elsevier It occurs in nature with two different crystal structures as the rare m ...
. Many minerals and ores are monosulfides.[Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. .]
Dichalcogenides
Metal dichalcogenides have the formula ME2, where M = a transition metal and E = S, Se, Te.[Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. .] The most important members are the sulfides. They are always dark diamagnetic solids, insoluble in all solvents, and exhibit semiconducting
A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
properties. Some are supeconductors.
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
Titanium disulfide is an inorganic compound with the formula Ti S2. A golden yellow solid with high electrical conductivity, it belongs to a group of compounds called transition metal dichalcogenides, which consist of the stoichiometry M E2. ...
was investigated in prototype cathode
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...
s for secondary batteries, exploiting its ability to reversibly undergo intercalation by lithium
Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
. Molybdenum disulfide is the subject of thousand articles and the main ore of molybdenum, termed molybdenite
Molybdenite is a mineral of molybdenum disulfide, Mo S2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum ato ...
. It is used as a solid lubricant
Dry lubricants or solid lubricants are materials that, despite being in the solid phase, are able to reduce friction between two surfaces sliding against each other without the need for a liquid oil medium.
The two main dry lubricants are graphit ...
and catalyst for hydrodesulfurization
Hydrodesulfurization (HDS) is a catalytic chemical process widely used to remove sulfur (S) from natural gas and from refined petroleum products, such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils. The purpose of remov ...
. 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
Molybdenum disulfide (or moly) is an inorganic compound composed of molybdenum and sulfur. Its chemical formula is .
The compound is classified as a transition metal dichalcogenide. It is a silvery black solid that occurs as the mineral molybdenit ...
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. 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 alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
. 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.
Pyrite and related disulfides
In contrast to classical metal dichalcogenides, iron pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic luster and pale brass-yellow hue giv ...
, a common mineral, is usually described as consisting of Fe2+ and the persulfido anion S22−. The sulfur atoms within the disulfido dianion are bound together via a short S-S bond. "Late" transition metal disulfides (Mn, Fe, Co, Ni) almost always adopt the pyrite or the related marcasite
The mineral marcasite, sometimes called “white iron pyrite”, is iron sulfide (FeS2) with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both ...
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 Tetrathiomolybdate, also spelled tiomolibdate (USAN), is the anion of the following salts:
* Ammonium tetrathiomolybdate, a building block in bioinorganic chemistry
* Bis-choline tetrathiomolybdate
Tiomolibdic acid (trade name Decuprate) is a c ...
with acid:
:MoS42− + 2 H+ → MoS3 + H2S
The mineral patrónite
Patronite is the vanadium sulfide mineral with formula V S4. The material is usually described as V4+(S22−)2. Structurally, it is a "linear-chain" compound with alternating bonding and nonbonding contacts between the vanadium centers. The ...
, 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.[
]
Main group chalcogenides
:
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.[
The chalcogen is assigned positive oxidation states for the halides, nitrides, and oxides.
]
See also
*Phase-change memory
Phase-change memory (also known as PCM, PCME, PRAM, PCRAM, OUM (ovonic unified memory) and C-RAM or CRAM (chalcogenide RAM)) is a type of non-volatile random-access memory. PRAMs exploit the unique behaviour of chalcogenide glass. In PCM, heat pr ...
*Chalcogen
The chalcogens (ore forming) ( ) 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 radioact ...
*Negative resistance
In electronics, negative resistance (NR) is a property of some electrical circuits and devices in which an increase in voltage across the device's terminals results in a decrease in electric current through it.
This is in contrast to an ordi ...
*Chalcogenide glass
Chalcogenide glass (pronounced hard ''ch'' as in ''chemistry'') is a glass containing one or more chalcogens (sulfur, selenium and tellurium, but excluding oxygen). Such glasses are covalently bonded materials and may be classified as covalent netw ...
*Hydrogen chalcogenide Hydrogen chalcogenides (also chalcogen hydrides or hydrogen chalcides) are binary compounds of hydrogen with chalcogen atoms (elements of group 16: oxygen, sulfur, selenium, tellurium, and polonium). Water, the first chemical compound in this series ...
*Carbon dichalcogenide Carbon dichalcogenides are chemical compounds of carbon and chalcogen elements. They have the general chemical formula CZ2, where Z = O, S, Se, Te.
This includes:
* Carbon dioxide,
* Carbon disulfide,
* Carbon diselenide,
* Carbonyl sulfide, O ...
References
External links
Advanced Chalcogenide Technologies and Applications Lab
''ACTAlab'' Jun 14, 2016
Phase change memory-based 'moneta' system points to the future of computer storage
''ScienceBlog'' Jun 03, 2011
*{{cite journal , last1 = Kovalenko , first1 = Maksym V. , last2 = Scheele , first2 = Marcus , last3 = Talapin , first3 = Dmitri V. , title = Colloidal Nanocrystals with Molecular Metal Chalcogenide Surface Ligands , journal = Science , year = 2009 , volume = 324 , issue = 5933 , pages = 1417–1420 , doi=10.1126/science.1170524, pmid = 19520953 , bibcode = 2009Sci...324.1417K, s2cid = 21845356
Big Blue boffins hatch dirt-cheap solar cells
The Register, 12 February 2010