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, Se2−, is prevalent only in very basic conditions. In neutral conditions, hydrogen selenide ion, HSe, is most common. In acid conditions, hydrogen selenide, H2Se, is formed.

Some selenides are reactive to oxidation by air. Owing to the greater reducing power of selenide, metal selenides are more easily decomposed to the elements than are sulfides (tellurides are even more labile). Selenides of electropositive metals: such as aluminium selenide readily hydrolyse, even in moist air, evolving toxic hydrogen selenide gas.

Pure selenide minerals are rare, instead selenium tends to partially substitute for sulfide in many sulfide minerals. The degree of substitution is only of commercial interest for copper sulfide ores, in which case selenium is recovered as a by-product of copper refining. Some selenide minerals include ferroselite and umangite.[1]

Polyselenides

Polyselenide anions are chains with the composition Se2−
n
. Polyselenides also refer to salts of these anions. They are commonly synthesized by melting elements together in a quartz tube. Selenium and an alkali metal react to initially give white, sparingly soluble solids like monoselenides. Excess selenium leads to the formation of soluble diselenides and very soluble polyselenides with even greater amounts of selenium. Alternatively, they can be prepared by dissolving selenium and an alkali metal in a liquid ammonia.[2] Synthesis can also be conducted in high-boiling, polar, aprotic solvents such as DMF, HMPA, and NMP.[3] Aqueous polyselenides undergo salt metathesis with large organic counterions to form crystalline salts that are soluble in organic solvents.

2 Na + n Se → Na2Sen
Na2Sen + 2 R4NCl → (R4N)2Sen + 2 NaCl

The structures of polyselenides have been examined by X-ray crystallography. One characteristic feature of the structure is that two terminal Se–Se bonds are shorter than those bonds involving internal selenium atoms. High resolution solid state 77Se NMR spectroscopy of for [NMe4]2Se5 and [NMe4]2Se6 suggest similar confirmations of the anions [Se5]2− and Se2− in the solid state and in solution. The spectra of [NMe4]2Se5 show five distinct selenium sites and the [NMe4]2Se6 spectra show symmetry with only 3 crystallographically different selenium sites. Single-crystal X-ray structure determination of the two salts support the NMR data.[4]

Reactivity

Polyselenides are prone to decomposition on exposure to air, in which case they are oxidized back to elemental selenium.

Se2−
n
+ 2 H+ + ​12 O2n Se + H2O

Polyselenides form metal complexes. Sex (x = 4, 5, 6) function as chelating ligands in complexes, e.g. (C5H5)2TiSe5, which is analogous to titanocene pentasulfide.[2] Polyselenide anions reacts with organic halides:

2 RX + Se2−
2
→ R2Se2 + 2 X

Metal selenide quantum dots

Colloidal nanoparticle of lead sulfide (selenide) with complete passivation
Core shell sulfide/selenide quantum dot

Metal selenide quantum dots and nanoparticles can be prepared by a variety of synthetic methods are available, many of which require high temperatures and hazardous precursor compounds.[5] The particles can be adapted for a variety of applications by varying the ligands coordinated to the positively-charged outer layer. Many ligand-exchange reactions are available for use, trading X, L, and Z-type ligands, the mechanism for which is still under study.[6]

Applications

Quantum dots based on metal selenides have been extensively for their distinctive spectral properties.[7] Core-shell alloys of cadmium sulfide and selenide are of interest in imaging and phototherapy.[8]

Examples

References

  1. ^ Bernd E. Langner "Selenium and Selenium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a23_525.
  2. ^ a b Kolis, J. "Coordination Chemistry of Polychalcogen Anions and Transition Metal Carbonyls" Coordination Chemistry Reviews 1990, volume 105, pp. 195-219. doi:10.1016/0010-8545(90)80023-M
  3. ^ Thompson, D.; Boudjouk, P. A :Convenient Synthesis of Alkali Metal Selenides and Diselenides in Tetrahydrofuran and the Reactivity Differences Exhibited By These Salts Toward Organic Bromides" Journal of Organic Chemistry 1988, volume 53, pp. 2109-2112. doi: 10.1021/jo00244a051
  4. ^ Barrie, P. J.; Clark, R. J. H.; Selenium Solid-State NMR Spectroscopy and Structures of Tetramethylammonium Pentaselenide and Hexaselenide Complexes. Inorg. Chem, 1995, 34, 4299–4304 DOI: 10.1021/ic00121a006
  5. ^ Chen, Ou; Chen, Xian; Yang, Yongan; Lynch, Jared; Wu, Huimeng; Zhuang, Jiaqi; Cao, Y. Charles (2008). "Synthesis of Metal-Selenide Nanocrystals Using Selenium Dioxide as the Selenium Precursor". Angewandte Chemie International Edition. 47 (45): 8638–8641. doi:10.1002/anie.200804266. ISSN 1433-7851. PMID 18850601.
  6. ^ Anderson, Nicholas C.; Owen, Jonathan S. (2013-01-08). "Soluble, Chloride-Terminated CdSe Nanocrystals: Ligand Exchange Monitored by 1H and 31P NMR Spectroscopy". Chemistry of Materials. 25 (1): 69–76. doi:10.1021/cm303219a. ISSN 0897-4756.
  7. ^ Larson, Daniel R.; Zipfel, Warren R.; Williams, Rebecca M.; Clark, Stephen W.; Bruchez, Marcel P.; Wise, Frank W.; Webb, Watt W. (2003-05-30). "Water-Soluble Quantum Dots for Multiphoton Fluorescence Imaging in Vivo". Science. 300 (5624): 1434–1436. Bibcode:2003Sci...300.1434L. doi:10.1126/science.1083780. ISSN 0036-8075. PMID 12775841.
  8. ^ Hessel, Colin M.; Pattani, Varun P.; Rasch, Michael; Panthani, Matthew G.; Koo, Bonil; Tunnell, James W.; Korgel, Brian A. (2011-06-08). "Copper Selenide Nanocrystals for Photothermal Therapy". Nano Letters. 11 (6): 2560–2566. Bibcode:2011NanoL..11.2560H. doi:10.1021/nl201400z. ISSN 1530-6984. PMC 3111000. PMID 21553924.

External links

Aluminium selenide

Aluminium selenide is the inorganic compound with the formula Al2Se3.

Antimony triselenide

Antimony triselenide is the chemical compound with the formula Sb2Se3. The material exists as the sulfosalt mineral antimonselite, which crystallizes in an orthorhombic space group. In this compound, antimony has the oxidation state +3 and selenium −2, but in fact the bonding in this compound is highly covalent as reflected by the black color and semiconducting properties of this and related materials.It may be formed by the reaction of antimony with selenium.

Arsenic triselenide

Arsenic triselenide (As2Se3) is an inorganic chemical compound, a selenide of arsenic.

Amorphous arsenic triselenide is used as a chalcogenide glass for infrared optics, as it transmits light with wavelengths between 870 nm and 17.2 µm [reference needed].

Arsenic triselenide is covalently bonded. Even so, the arsenic has a formal oxidation state of +3.

Bismuth selenide

Bismuth selenide (Bi2Se3) is a gray compound of bismuth and selenium also known as bismuth(III) selenide. It is a semiconductor and a thermoelectric material. While perfect stoichiometric bismuth selenide should be a semiconductor (with a gap of 0.3 eV) naturally occurring selenium vacancies act as electron donors and it often acts as a semimetal. Topologically protected surface states have been observed in Bismuth selenide, which is the subject of ongoing scientific research.

Cadmium selenide

Cadmium selenide is an inorganic compound with the formula CdSe. It is a black to red-black solid that is classified as a II-VI semiconductor of the n-type. Much of the current research on cadmium selenide is focused on its nanoparticles.

Calcium selenide

Calcium selenide (CaSe) is a chemical compound consisting of the elements calcium and selenium in equal stoichiometric ratio.

Chromium(II) selenide

Chromium(II) selenide is an inorganic compound with the chemical formula CrSe.

Cobalt(II) selenide

Cobalt(II) selenide is an inorganic compound with the chemical formula CoSe.

Copper indium gallium selenide

Copper indium gallium (di)selenide (CIGS) is a I-III-VI2 semiconductor material composed of copper, indium, gallium, and selenium. The material is a solid solution of copper indium selenide (often abbreviated "CIS") and copper gallium selenide. It has a chemical formula of CuIn(1-x)Ga(x)Se2 where the value of x can vary from 0 (pure copper indium selenide) to 1 (pure copper gallium selenide). CIGS is a tetrahedrally bonded semiconductor, with the chalcopyrite crystal structure, and a bandgap varying continuously with x from about 1.0 eV (for copper indium selenide) to about 1.7 eV (for copper gallium selenide).

Copper indium gallium selenide solar cells

A copper indium gallium selenide solar cell (or CIGS cell, sometimes CI(G)S or CIS cell) is a thin-film solar cell used to convert sunlight into electric power. It is manufactured by depositing a thin layer of copper, indium, gallium and selenium on glass or plastic backing, along with electrodes on the front and back to collect current. Because the material has a high absorption coefficient and strongly absorbs sunlight, a much thinner film is required than of other semiconductor materials.

CIGS is one of three mainstream thin-film PV technologies, the other two being cadmium telluride and amorphous silicon. Like these materials, CIGS layers are thin enough to be flexible, allowing them to be deposited on flexible substrates. However, as all of these technologies normally use high-temperature deposition techniques, the best performance normally comes from cells deposited on glass, even though advances in low-temperature deposition of CIGS cells have erased much of this performance difference. CIGS outperforms polysilicon at the cell level, however its module efficiency is still lower, due to a less mature upscaling.Thin-film market share is stagnated at around 15 percent, leaving the rest of the PV market to conventional solar cells made of crystalline silicon. In 2013, the market share of CIGS alone was about 2 percent and all thin-film technologies combined fell below 10 percent. CIGS cells continue being developed, as they promise to reach silicon-like efficiencies, while maintaining their low costs, as is typical for thin-film technology. Prominent manufacturers of CIGS photovoltaics were the now-bankrupt companies Nanosolar and Solyndra. Current market leader is the Japanese company Solar Frontier, Global Solar and GSHK Solar producing solar modules free of any heavy metals such as cadmium or lead.

Germanium selenide

Germanium selenide is a chemical compound with the formula GeSe. It exists as black crystalline powder having orthorhombic (distorted NaCl-type) crystal symmetry; at temperatures ~650 °C, it transforms into the cubic NaCl structure.To grow GeSe crystals, GeSe powder is vaporized at the hot end of a sealed ampule and allowed to condense at the cold end. Usual crystals are small and show signs of irregular growth, caused mainly by convective motion in the gaseous medium. However, GeSe grown under condition of zero-gravity and reduced convection aboard the Skylab are ~10 times larger than Earth-grown crystals, and are free from visual defects.

Hydrogen selenide

Hydrogen selenide is an inorganic compound with the formula H2Se. This hydrogen chalcogenide is the simplest and most commonly encountered hydride of selenium. H2Se is a colorless, flammable gas under standard conditions. It is the most toxic selenium compound with an exposure limit of 0.05 ppm over an 8-hour period. Even at extremely low concentrations, this compound has a very irritating smell resembling that of decayed horseradish or 'leaking gas', but smells of rotten eggs at higher concentrations.

Iron(II) selenide

Iron(II) selenide refers to a number of inorganic compounds of ferrous iron and selenide (Se2−). The phase diagram of the system Fe–Se reveals the existence of several non-stoichiometric phases between ~49 at. % Se and ~53 at. % Fe, and temperatures up to ~450 °C. The low temperature stable phases are the tetragonal PbO-structure (P4/nmm) β-Fe1−xSe and α-Fe7Se8. The high temperature phase is the hexagonal, NiAs structure (P63/mmc) δ-Fe1−xSe. Iron (II) selenide occurs naturally as the NiAs-structure mineral achavalite.

More selenium rich iron selenide phases are the γ phases (γ and γˈ), assigned the Fe3Se4 stoichiometry, and FeSe2, which occurs as the marcasite-structure natural mineral feroselite, or the rare pyrite-structure mineral dzharkenite.

It is used in electrical semiconductors.

Lead selenide

Lead selenide (PbSe), or lead(II) selenide, a selenide of lead, is a semiconductor material. It forms cubic crystals of the NaCl structure; it has a direct bandgap of 0.27 eV at room temperature. (Note that incorrectly identifies PbSe and other IV–VI semiconductors as indirect gap materials.) It is a grey crystalline solid material.

It is used for manufacture of infrared detectors for thermal imaging, operating at wavelengths between 1.5–5.2 µm. It does not require cooling, but performs better at lower temperatures. The peak sensitivity depends on temperature and varies between 3.7–4.7 µm.Single crystal nanorods and polycrystalline nanotubes of lead selenide have been synthesized via controlled organism membranes. The diameter of the nanorods were approx. 45 nm and their length was up to 1100 nm, for nanotubes the diameter was 50 nm and the length up to 2000 nm.Lead selenide nanocrystals embedded into various materials can be used as quantum dots, for example in nanocrystal solar cells.

Lead selenide is a thermoelectric material. The material was identified as a potential high temperature thermoelectric with sodium or chlorine doping by Alekseva and co-workers at the A.F. Ioffe Institute in Russia. Subsequent theoretical work at Oak Ridge National Laboratory, USA predicted that its p-type performance could equal or exceed that of the sister compound, lead telluride. Several groups have since reported thermoelectric figures of merit exceeding unity, which is the characteristic of a high performance thermoelectric.The mineral clausthalite is a naturally occurring lead selenide.

It may be formed by direct reaction between its constituent elements (lead and selenium).

Manganese(II) selenide

Managnese(II) selenide is an inorganic compound with the chemical formula MnSe.

Mercury selenide

Mercury selenide (HgSe) is a chemical compound of mercury and selenium. It is a grey-black crystalline solid semi-metal with a sphalerite structure. The lattice constant is 0.608 nm.

Mercury selenide can also refer to the following chemical compounds: HgSe2 and HgSe8. HgSe is strictly mercury(II) selenide.

HgSe occurs naturally as the mineral Tiemannite.

Along with other II-VI compounds, colloidal nanocrystals of HgSe can be formed.

Silver(I) selenide

Silver selenide (Ag2Se) is the reaction product formed when selenium toning analog silver gelatine photo papers in photographic print toning. The selenium toner contains sodium selenite (Na2SeO3) as one of its active ingredients, which is the source of the selenide (Se2−) anion combining with the silver in the toning process.

It is found in nature as the mineral naumannite, a comparatively rare silver mineral which has nevertheless become recognized as important silver compound in some low-sulfur silver ores from mines in Nevada and Idaho.

Sodium selenide

Sodium selenide is an inorganic compound of sodium and selenium with the chemical formula Na2Se.

Zinc selenide

Zinc selenide (ZnSe) is a light-yellow, solid compound comprising zinc (Zn) and selenium (Se). It is an intrinsic semiconductor with a band gap of about 2.70 eV at 25 °C (77 °F). ZnSe rarely occurs in nature, and is found in the mineral that was named after Hans Stille called "stilleite."

Selenides

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