{{Greenwood&Earnshaw2nd}} consistently distinguishes oxides from chalcogenides |
rephrase for clarity, comment on covalency |
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:[[image:Cadmium sulfide.jpg|thumb|220px|Cadmium sulfide, a prototypical metal chalcogenide, is used as a yellow pigment.]] |
:[[image:Cadmium sulfide.jpg|thumb|220px|Cadmium sulfide, a prototypical metal chalcogenide, is used as a yellow pigment.]] |
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A '''chalcogenide''' is a chemical compound consisting of at least one [[chalcogen]] [[anion]] and at least one more [[electropositive]] element. Although all [[group 16 element]]s of the periodic table are defined as chalcogens, the term chalcogenide is more commonly reserved for [[sulfide]]s, [[selenide]]s, and [[Telluride (chemistry)|telluride]]s, rather than [[oxide]]s.<ref |
A '''chalcogenide''' is a chemical compound consisting of at least one [[chalcogen]] [[anion]] and at least one more [[electropositive]] element. Although all [[group 16 element]]s of the periodic table are defined as chalcogens, the term chalcogenide is more commonly reserved for [[sulfide]]s, [[selenide]]s, and [[Telluride (chemistry)|telluride]]s, rather than [[oxide]]s.<ref name=Greenwood/> Many metal ores exist a chalcogenides. [[photoconductivity|Photoconductive]] [[chalcogenide glass]]es are used in [[xerography]]. Some pigments and catalysts are also based on chalcogenides. The the metal dichalcogenide [[Molybdenum disulfide|MoS<sub>2</sub>]] is common [[solid lubricant]]. |
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==Alkali metal and alkaline earth chalcogenides== |
==Alkali metal and alkaline earth chalcogenides== |
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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<sup>-</sup>) anions. |
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<sup>-</sup>) anions. The alkali metal chalcogenides often crystallize with the anti[[fluorite]] structure and the alkaline earth salts in the [[sodium chloride]] motif. |
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:[[Image:Sphalerite-unit-cell-3D-balls.png|thumb|left|200px|The zinc blende structure is a common motif for metal monochalcogenides.]] |
:[[Image:Sphalerite-unit-cell-3D-balls.png|thumb|left|200px|The zinc blende structure is a common motif for metal monochalcogenides.]] |
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==Transition metal chalcogenides== |
==Transition metal chalcogenides== |
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Transition metal chalcogenides occur with many stoichiometries and many structures. 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. Ta<sub>2</sub>S), which exhibit extensive metal-metal bonding,<ref>Timothy Hughbanks "Exploring the metal-rich chemistry of the early transition elements" Journal of Alloys and Compounds 1995, vol. 229, pp. 40-53. http://dx.doi.org/10.1016/0925-8388(95)01688-0</ref> and chalcogenide-rich materials such as Re<sub>2</sub>S<sub>7</sub>, which features extensive chalcogen-chalcogen bonding. |
Transition metal chalcogenides occur with many stoichiometries and many structures. 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. Ta<sub>2</sub>S), which exhibit extensive metal-metal bonding,<ref>Timothy Hughbanks "Exploring the metal-rich chemistry of the early transition elements" Journal of Alloys and Compounds 1995, vol. 229, pp. 40-53. http://dx.doi.org/10.1016/0925-8388(95)01688-0</ref> and chalcogenide-rich materials such as Re<sub>2</sub>S<sub>7</sub>, which features extensive chalcogen-chalcogen bonding. |
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For the purpose of classifying these materials, the chalcogenide is often viewed as a dianion. In fact, transition metal chalcogenides are highly [[covalent], not ionic, as indicated by their semiconducting properties. |
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===Monochalcogenides=== |
===Monochalcogenides=== |
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====Pyrite and related disulfides==== |
====Pyrite and related disulfides==== |
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In contrast to classical metal dichalcogenides, [[iron pyrite]] is |
In contrast to classical metal dichalcogenides, [[iron pyrite]], a common mineral, is usually described as consisting of Fe<sub>2+</sub> and the persulfido anion S<sub>2</sub><sup>2-</sup>. The sulfur atoms within the disulfido dianion are bound together via a short S-S bond.<ref>Vaughan, D. J.; Craig, J. R. “Mineral Chemistry of Metal Sulfides" Cambridge University Press, Cambridge: 1978. ISBN 0521214890.</ref> "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. |
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==Main group chalcogenides== |
==Main group chalcogenides== |
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Chalcogen derivatives |
Chalcogen derivatives are known for all of the [[main group element]]s except the noble gases. Usually, their stoichiometries follow the classical valence trends, e.g. SiS<sub>2</sub>, B<sub>2</sub>S<sub>3</sub>, Sb<sub>2</sub>S<sub>3</sub>. Many exceptions exist however, e.g. [[Phosphorus sesquisulfide|P<sub>4</sub>S<sub>3</sub>]], an ingredient in strike-anywhere matches. The structures of many of main group materials are dictated, not by close packing, but by directional covalent bonding.<ref name=Greenwood/> |
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The chalcogen is assigned positive oxidation states for the halides, nitrides, and oxides. These compounds |
The chalcogen is assigned positive oxidation states for the halides, nitrides, and oxides. These compounds, e.g., SCl<sub>2</sub>, are not usually classified as chalcogenides. |
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:[[Image:Orpiment-unit-cell-3D.png|thumb|left|As<sub>2</sub>S<sub>3</sub> is a polymer where the As and S centers obey the [[octet rule]].]] |
:[[Image:Orpiment-unit-cell-3D.png|thumb|left|As<sub>2</sub>S<sub>3</sub> is a crosslinked [[polymer]] where the As and S centers obey the [[octet rule]].]] |
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==See also== |
==See also== |
Revision as of 12:40, 18 October 2013
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, and tellurides, rather than oxides.[1] Many metal ores exist a chalcogenides. Photoconductive chalcogenide glasses are used in xerography. Some pigments and catalysts are also based on chalcogenides. The the metal dichalcogenide MoS2 is common 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.
Transition metal chalcogenides
Transition metal chalcogenides occur with many stoichiometries and many structures. 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,[2] 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. In fact, transition metal chalcogenides are highly [[covalent], not ionic, as indicated by their semiconducting properties.
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 very 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. Important monochalcogenides include some pigments, notably cadmium sulfide, and many minerals and ores.[1]
Dichalcogenides
Metal dichalcogenides have the formula ME2, where M = a transition metal and E = S, Se, Te.[3] As usual, the most important members are the sulfides. They are always dark diamagnetic solids, insoluble in all solvents, and exhibiting semiconducting properties. 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, the subject of many thousand publications, is the main ore of molybdenum where it is called 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 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).
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 disulfido dianion are bound together via a short S-S bond.[4] "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.
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, an ingredient in strike-anywhere matches. The structures of many of main group materials are dictated, not by close packing, but by directional covalent bonding.[1]
The chalcogen is assigned positive oxidation states for the halides, nitrides, and oxides. These compounds, e.g., SCl2, are not usually classified as chalcogenides.
See also
References
- ^ a b c d Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
- ^ Timothy Hughbanks "Exploring the metal-rich chemistry of the early transition elements" Journal of Alloys and Compounds 1995, vol. 229, pp. 40-53. http://dx.doi.org/10.1016/0925-8388(95)01688-0
- ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
- ^ Vaughan, D. J.; Craig, J. R. “Mineral Chemistry of Metal Sulfides" Cambridge University Press, Cambridge: 1978. ISBN 0521214890.
External links
- Phase change memory-based 'moneta' system points to the future of computer storage ScienceBlog Jun 03, 2011
- Tiny Chip Demonstrates Big Memory in Cosmos Michael P. Kleiman for Air Force Research Laboratory, Space Vehicles Directorate (SpaceDaily) Jul 27, 2006
- Breakthrough switching speed with an all-optical chalcogenide glass chip: 640 Gbit/s demultiplexing Michael Galili, Jing Xu, Hans C. Mulvad, Leif K. Oxenløwe, Anders T. Clausen, Palle Jeppesen, Barry Luther-Davis, Steve Madden, Andrei Rode, Duk-Yong Choi, Mark Pelusi, Feng Luan, and Benjamin J. Eggleton (Optics Express, Vol. 17, Issue 4, pp. 2182–2187) February 2, 2009
- Maksym V. Kovalenko, Marcus Scheele, and Dmitri V. Talapin. "Colloidal Nanocrystals with Molecular Metal Chalcogenide Surface Ligands". Science 324(12June2009): 1417-1420
- Big Blue boffins hatch dirt-cheap solar cells The Register, 12 February 2010