Anions

thumb|right|The Crystal structure#Unit cell|unit cell of [[rutile, an important oxide of titanium. Ti(IV) centers are grey; oxygen centers are red. Notice that oxygen forms three bonds to titanium and titanium forms six bonds to oxygen.]] 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 (anion bearing a net charge of −2) 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 coati

The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pronunciation of the word "chloride" is .

thumb|Lattice structure of titanium carbide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece.

Sulfide (also sulphide in British English) 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 large families of inorganic and organic compounds, e.g. lead sulfide and dimethyl sulfide. Hydrogen sulfide (H2S) and bisulfide (HS−) are the conjugate acids of sulfide.

In chemistry, a hydride is formally the anion of hydrogen (H−), a hydrogen ion with two electrons. In modern usage, this is typically only used for ionic bonds, but it is sometimes (and has been more frequently in the past) applied to all compounds containing covalently bound H atoms. In this broad and potentially archaic sense, water (H2O) is a hydride of oxygen, ammonia is a hydride of nitrogen, etc. In covalent compounds, it implies hydrogen is attached to a less electronegative element. In such cases, the H centre has nucleophilic character, which contrasts with the protic character

Fluoride () is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts typically have distinctive bitter tastes and are odorless. Its salts and minerals are important chemical reagents and industrial chemicals, mainly used in the production of hydrogen fluoride for fluorocarbons. Fluoride is classified as a weak base, since it only partially associates in solution, but concentrated fluoride is corrosive and can attack the skin.

An iodide ion is I−. Compounds with iodine in formal oxidation state −1 are called iodides. In everyday life, iodide is most commonly encountered as a component of iodized salt, which many governments mandate. Worldwide, iodine deficiency affects two billion people and is the leading preventable cause of intellectual disability.

In chemistry, a nitride is a chemical compound of nitrogen. Nitrides can be inorganic or organic, ionic or covalent. The nitride anion, N3−, is very elusive but compounds of nitride are numerous, although rarely naturally occurring. Some nitrides have a found applications, such as wear-resistant coatings (e.g., titanium nitride, TiN), hard ceramic materials (e.g., silicon nitride, Si3N4), and semiconductors (e.g., gallium nitride, GaN). The development of GaN-based light emitting diodes was recognized by the 2014 Nobel Prize in Physics. Metal nitrido complexes are also common.

In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula . The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of the one-electron reduction of dioxygen , which occurs widely in nature. Molecular oxygen (dioxygen) is a diradical containing two unpaired electrons, and superoxide results from the addition of an electron which fills one of the two degenerate molecular orbitals, leaving a charged ionic species with a single unpaired electron and a net negative charge of −

In organic chemistry, a carbanion is an anion with a lone pair attached to a tervalent carbon atom. This gives the carbon atom a negative charge.

In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate () and tetrasodium pyrophosphate (), among others. Often pyrophosphates are called diphosphates. The parent pyrophosphates are derived from partial or complete neutralization of pyrophosphoric acid. The pyrophosphate bond is also sometimes referred to as a phosphoanhydride bond, a naming convention which emphasizes the loss of water that occurs when two phosphates form a new bond, and which mirrors the nomenclature for anhyd

thumb|A portion of the structure of , highlighting the highly crosslinked nature common to many transition metal phosphides (Cu = orange, P = purple). In chemistry, a phosphide is a compound containing the ion or its equivalent. Many different phosphides are known, with widely differing structures. Most commonly encountered on the binary phosphides, i.e. those materials consisting only of phosphorus and a less electronegative element. Numerous are polyphosphides, which are solids consisting of anionic chains or clusters of phosphorus. Phosphides are known with the majority of less electronegat

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.

thumb|220px|The compound Titanocene pentasulfide| is an example of a polysulfide complex Polysulfides are a class of chemical compounds derived from anionic chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic. The inorganic polysulfides have the general formula . These anions are the conjugate bases of polysulfanes . Organic polysulfides generally have the formulae , where R is an alkyl or aryl group.

thumb|155px|Carboxylate ion

negative ion of hydrogen

200px|Structure of titanium disilicide (Ti = white spheres).|thumb|right A silicide is a type of chemical compound that combines silicon and a usually more electropositive element.

In chemistry, an acetylide is a compound that can be viewed as the result of replacing one or both hydrogen atoms of acetylene (ethyne) by metallic or other cations. Calcium carbide is an important industrial compound, which has long been used to produce acetylene for welding and illumination. It is also a major precursor to vinyl chloride. Other acetylides are reagents in organic synthesis.

Ferricyanide is the name of the anion . It is also called hexacyanoferrate(III) and in rare, but systematic nomenclature, hexacyanidoferrate(III). The most common salt of this anion is potassium ferricyanide, a red crystalline material that is used as an oxidant in organic chemistry.

Antimonides (sometimes called stibnides or stibinides) are compounds of antimony with more electropositive elements. The antimonide ion is but the term refers also to any anionic derivative of antimony.

right|150px|thumb|Triflate group right|150px|thumb|Triflate anion

An alkalide is a chemical compound in which alkali metal atoms are anions (negative ions) with a charge or oxidation state of −1. Until the first discovery of alkalides in the 1970s, alkali metals were known to appear in salts only as cations (positive ions) with a charge or oxidation state of +1. These types of compounds are of theoretical interest due to their unusual stoichiometry and low ionization potentials. Alkalide compounds are chemically related to the electrides, salts in which trapped electrons are effectively the anions.

thumb|right|140px|Ball-and-stick model of the tetrahydroborate anion,

Cuprates are a class of compounds that contain copper (Cu) atom(s) in an anion. The term 'cuprate' itself originates from 'cuprum', the Latin word for copper. Cuprates appear mainly in three contexts: anionic organocopper species; inorganic, anionic coordination complexes; and complex oxides.

The bifluoride ion is an inorganic anion with the chemical formula . The anion is colorless. Salts of bifluoride are commonly encountered in the reactions of fluoride salts with hydrofluoric acid. The commercial production of fluorine involves electrolysis of bifluoride salts.

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. Bisulfide solutions are corrosive and attack the skin.

Thiophosphates (or phosphorothioates, PS) are chemical compounds and anions with the general chemical formula (x = 0, 1, 2, or 3) and related derivatives where organic groups are attached to one or more O or S. Thiophosphates feature tetrahedral phosphorus(V) centers.

thumb|right|150px|General chemical structure of a nitronate

anion

In chemistry, triiodide usually refers to the triiodide ion, . This anion, one of the polyhalogen ions, is composed of three iodine atoms. It is formed by combining aqueous solutions of iodide salts and iodine. Some salts of the anion have been isolated, including thallium(I) triiodide (Tl+[I3]−) and ammonium triiodide ([NH4]+[I3]−). Triiodide is observed to be a red colour in solution.

Tetraphenylborate is an organoboron anion consisting of a central boron atom with four phenyl groups. It is a colorless anion that forms water-insoluble salts with a variety of cations. It was considered as a precipitant for caesium-137 ions in the context of radiowaste cleanup.

right|thumb|Before: Toluene is refluxed with sodium-benzophenone to dry and deoxygenate it. right|thumb|After: The deep blue coloration of the benzophenone ketyl radical shows that the toluene to be distilled is dry and oxygen-free. A ketyl group in organic chemistry is an anion radical that contains a group R2C−O•. It is the product of the 1-electron reduction of a ketone.

Ferrate loosely refers to a material that can be viewed as containing anionic iron complexes. The term ferrate derives .

Tetranitratoborate is an anion composed of boron with four nitrate groups. It has formula . It can form salts with large cations such as tetramethylammonium nitratoborate, or tetraethylammonium tetranitratoborate. The ion was first discovered by C. R. Guibert and M. D. Marshall in 1966 after failed attempts to make neutral (non-ionic) boron nitrate, , which has resisted attempts to make it; if it exists, it is unstable above −78 °C.

thumb|right|A space-filling representation of the crystal structure of magnesium polonide: Mg2+ ions are shown in green, while Po2− ions are shown in brown. thumb|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 are amongst the most chemically stable compounds of polonium, and can be divided into two broad groups: ionic polonides, which appear to contain the Po2− anion; intermetallic polonides

The polyiodides are a class of polyhalogen anions composed entirely of iodine atoms. The most common member is the triiodide ion, . Other known larger polyiodides include [I4]2−, [I5]−, [I6]2−, [I7]−, [I8]2−, [I9]−, [I10]2−, [I10]4−, [I11]3−, [I12]2−, [I13]3−, [I14]4-, [I16]2−, [I22]4−, [I26]3−, [I26]4−, [I28]4− and [I29]3−. All these can be considered as formed from the interaction of the I–, I2, and building blocks.

best known structural form for heteropoly acids

group of isomeric chemical compounds

The bismuthide ion is but the term is often used to describe less reduced forms of bismuth.

Tetrahydroxyborate is an inorganic anion with the chemical formula or . It contributes no colour to tetrahydroxyborate salts. It is found in the mineral hexahydroborite, , originally formulated . It is one of the boron oxoanions, and acts as a weak base. The systematic names are tetrahydroxyboranuide (substitutive) and tetrahydroxidoborate(1−) (additive). It can be viewed as the conjugate base of boric acid.

Azanide is the IUPAC-sanctioned name for the anion . The term is obscure; derivatives of are almost invariably referred to as amides, despite the fact that amide also refers to the organic functional group –. The anion is the conjugate base of ammonia, so it is formed by the self-ionization of ammonia. It is produced by deprotonation of ammonia, usually with strong bases or an alkali metal. Azanide has a H–N–H bond angle of 104.5°, nearly identical to the bond angle in the isoelectronic water molecule.

TRISPHAT (full name tris(tetrachlorocatecholato)phosphate(1−)) is an inorganic anion with the formula often prepared as the tributylammonium () or tetrabutylammonium ( salt. The anion features phosphorus(V) bonded to three tetrachlorocatecholate () ligands. This anion can be resolved into the axially chiral enantiomers, which are optically stable (the picture shows the Δ enantiomer).

The dodecaborate(12) anion, [B12H12]2−, is a boron hydride cluster anion. It forms a variety of colorless salts with alkali metal and quaternary ammonium cations. The cluster has a distinctive icosahedral structure with 12 boron atoms at the vertices, each boron atom is attached to a hydrogen atom. Its symmetry is classified by the molecular point group Ih.

anion

Ferrocyanide is the anion [Fe(CN)6]4−. Salts of this coordination complex give yellow solutions. It is usually available as the salt potassium ferrocyanide, which has the formula K4Fe(CN)6. [Fe(CN)6]4− is a diamagnetic species, featuring low-spin iron(II) center in an octahedral ligand environment. Although many salts of cyanide are highly toxic, ferro- and ferricyanides are less toxic because they tend not to release free cyanide. It is of commercial interest as a precursor to the pigment Prussian blue and, as its potassium salt, an anticaking agent.

A dianion is an anion with a net charge of −2. While there exist many stable molecular dianions, such as Tetrafluoroberyllate| and , thus far no stable atomic dianion has been found: Electron shielding and other quantum mechanical effects tend to make the addition of another electron to an atomic anion unstable.

aromatic species with a formula of [C8H8]2−, the dianion of cyclooctatetraene

[[Image:BARF.png|200px|right|thumb|The [BArF4]− anion with four fluorinated aryl (ArF) groups distributed tetrahedrally about a central boron atom.]] Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate is an anion with chemical formula [{3,5-(CF3)2C6H3}4B]−, which is commonly abbreviated as [BArF4]−, indicating the presence of fluorinated aryl (ArF = 3,5-bis(trifluoromethyl)phenyl) groups. It is sometimes referred to as ''Kobayashi's anion'' in honour of Hiroshi Kobayashi who led the team that first synthesised it. More commonly it is affectionately nicknamed "BARF". The BARF ion is also abbreviate

anion

Hexachloroplatinate is an anion with the chemical formula [PtCl6]2−.