In chemistry, there are three series of binary phosphorus halides, containing

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...

in the

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. ...

s +5, +3 and +2. All compounds have been described, in varying degrees of detail, although serious doubts have been cast on the existence of PI₅.I. Tornieporth-Getting & T. Klapötke, ''J. Chem. Soc.'', ''Chem. Commun.'' 1990, 132. Mixed

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 radioa ...

halides also exist.

Oxidation state +5 (PX₅)

In the gas phase the phosphorus pentahalides have

trigonal bipyramidal molecular geometry In chemistry, a trigonal bipyramid formation is a molecular geometry with one atom at the center and 5 more atoms at the corners of a triangular bipyramid. This is one geometry for which the bond angles surrounding the central atom are not ident ...

as explained by

VSEPR theory Valence shell electron pair repulsion (VSEPR) theory ( , ), is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. It is also named the Gillespie-Nyholm t ...

Phosphorus pentafluoride Phosphorus pentafluoride, P F5, is a phosphorus halide. It is a colourless, toxic gas that fumes in air. Preparation Phosphorus pentafluoride was first prepared in 1876 by the fluorination of phosphorus pentachloride using arsenic trifluoride, ...

is a relatively inert gas, notable as a mild

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

and a

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts ...

ion acceptor. It is a

fluxional molecule In chemistry and molecular physics, fluxional (or non-rigid) molecules are molecules that undergo dynamics such that some or all of their atoms interchange between symmetry-equivalent positions. Because virtually all molecules are fluxional in so ...

in which the axial (ax) and equatorial (eq) fluorine atoms interchange positions by the

Berry pseudorotation mechanism The Berry mechanism, or Berry pseudorotation mechanism, is a type of vibration causing molecules of certain geometries to isomerize by exchanging the two axial ligands (see Figure at right) for two of the equatorial ones. It is the most widely ac ...

Phosphorus pentachloride Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moist ...

phosphorus pentabromide Phosphorus pentabromide is a reactive, yellow solid of formula P Br5, which has the structure PBr4+ Br− in the solid state but in the vapor phase is completely dissociated to PBr3 and Br2. Rapid cooling of this phase to 15 K leads to for ...

, and

phosphorus heptabromide Phosphorus heptabromide is an inorganic compound with the formula PBr7. It is one of the phosphorus bromides. At normal conditions, it forms red prismatic crystals. PBr7 can be prepared by the sublimation of a mixture of phosphorus pentabromi ...

are ionic in the solid and liquid states; PCl₅ is formulated as PCl₄⁺PCl₆^–, but in contrast, PBr₅ is formulated as PBr₄⁺ Br⁻, and PBr₇ is formulated as PBr₄⁺ Br₃⁻. They are widely used as chlorinating and brominating agents in organic chemistry.

Oxidation state +3 (PX₃)

The phosphorus(III) halides are the best known of the three series. They are usually prepared by direct reaction of the elements, or by

transhalogenation Transhalogenation is a substitution reaction in which the halide of a halide compound is exchanged for another halide. Finkelstein reaction A common method is halide metathesis. An example is the conversion of alkyl chloride into alkyl fluoride: : ...

Phosphorus trifluoride Phosphorus trifluoride (formula P F3), is a colorless and odorless gas. It is highly toxic and reacts slowly with water. Its main use is as a ligand in metal complexes. As a ligand, it parallels carbon monoxide in metal carbonyls, and indeed ...

is used as a

ligand In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ele ...

coordination chemistry A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ''ligands'' or complexing ...

, where it resembles

carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

Phosphorus trichloride Phosphorus trichloride is an inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic a ...

is a major industrial chemical and widely used starting material for phosphorus chemistry.

Phosphorus tribromide Phosphorus tribromide is a colourless liquid with the formula P Br3. The liquid fumes in moist air due to hydrolysis and has a penetrating odour. It is used in the laboratory for the conversion of alcohols to alkyl bromides. Preparation PBr3 ...

is used in organic chemistry to convert

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

s to alkyl bromides and

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxyl ...

s to

acyl bromides In chemistry, an acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen atom and an alkyl group (). In organic chemistry, the acyl group ( ...

(''e.g.'' in the Hell-Volhard-Zelinsky reaction).

Phosphorus triiodide Phosphorus triiodide (PI3) is an inorganic compound with the formula PI3. A red solid, it is a common misconception that PI3 is too unstable to be stored; it is, in fact, commercially available. It is widely used in organic chemistry for convertin ...

also finds use in organic chemistry, as a mild oxygen acceptor. The trihalides are fairly readily oxidized by

s to give the corresponding

oxyhalides In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula , where X = fluorine (F), ...

or equivalents.

Oxidation state +2 (P₂X₄)

Phosphorus(II) halides may be prepared by passing an

electric discharge An electric discharge is the release and transmission of electricity in an applied electric field through a medium such as a gas (ie., an outgoing flow of electric current through a non-metal medium).American Geophysical Union, National Research ...

through a mixture of the trihalide vapour and

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

gas. The relatively stable P₂I₄ is known to have a ''trans'', bent configuration similar to

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazin ...

and finds some uses in organic syntheses, the others are of purely academic interest at the present time.

Diphosphorus tetrabromide Diphosphorus is an inorganic chemical with the chemical formula . Unlike nitrogen, its lighter pnictogen neighbor which forms a stable N2 molecule with a nitrogen to nitrogen triple bond, phosphorus prefers a tetrahedral form P4 because P-P pi-bo ...

is particularly poorly described. They are subhalides of phosphorus.

Oxyhalides,thiohalides and selehalides

The oxyhalides may be prepared from the corresponding trihalides by reaction with

organic peroxide In organic chemistry, organic peroxides are organic compounds containing the peroxide functional group (). If the R′ is hydrogen, the compounds are called hydroperoxides, which are discussed in that article. The O−O bond of peroxides easily ...

s or

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...

: they are sometimes referred to as phosphoryl halides. The thiohalides, also known as thiophosphoryl halides may be prepared from the trihalides by reaction with elemental

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

in an inert solvent. The corresponding selenohalides are also known. The oxyhalides and thiohalides are significantly more

electrophilic In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that car ...

than the corresponding phosphorus(III) species, and present a significant

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...

hazard.

References

{{reflist

External links

WebElementsNIST Standard Reference Database
Inorganic phosphorus compounds

Oxidation state +5 (PX5)