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 coordination chemistry, a ligand is an ion or molecule with a 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 el ...
in
metal complexes. As a ligand, it parallels
carbon monoxide
Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and 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 ...
in
metal carbonyls,
and indeed its toxicity is due to its binding with the
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
in blood
hemoglobin
Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...
in a similar way to carbon monoxide.
Physical properties
Phosphorus trifluoride has an F−P−F bond angle of approximately 96.3°.
Gaseous PF
3 has a
standard enthalpy of formation of −945 kJ/mol (−226
kcal/
mol). The phosphorus atom has a
nuclear magnetic resonance chemical shift of 97 ppm (downfield of
H3PO4).
Properties
Phosphorus trifluoride
hydrolyzes especially at
high pH, but it is less hydrolytically sensitive than
phosphorus trichloride. It does not attack glass except at high temperatures, and anhydrous
potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which utili ...
may be used to dry it with little loss. With hot
metal
A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...
s, phosphides and fluorides are formed. With
Lewis bases such as
ammonia
Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
addition products (adducts) are formed, and PF
3 is oxidized by
oxidizing agents such as
bromine
Bromine is a chemical element; it has chemical symbol, symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between th ...
or
potassium permanganate.
As a ligand for transition metals, PF
3 is a strong π-acceptor.
It forms a variety of
metal complexes with
metal
A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...
s in low
oxidation states. PF
3 forms several complexes for which the corresponding CO derivatives (see
metal carbonyl) are unstable or nonexistent. Thus, Pd(PF
3)
4 is known, but Pd(CO)
4 is not.
Such complexes are usually prepared directly from the related
metal carbonyl compound, with loss of
CO. However,
nickel metal
A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...
reacts directly with PF
3 at 100 °C under 35
MPa pressure to form Ni(PF
3)
4, which is analogous to
Ni(CO)4. Cr(PF
3)
6, the analogue of
Cr(CO)6, may be prepared from
dibenzenechromium:
:
Cr(C6H6)2 + 6 PF
3 → Cr(PF
3)
6 + 2
C6H6
Preparation
Phosphorus trifluoride is usually prepared from
phosphorus trichloride via halogen exchange using various
fluoride
Fluoride (). According to this source, is a possible pronunciation in British English. is an Inorganic chemistry, inorganic, Monatomic ion, monatomic Ion#Anions and cations, anion of fluorine, with the chemical formula (also written ), whose ...
s such as
hydrogen fluoride,
calcium fluoride,
arsenic trifluoride,
antimony trifluoride, or
zinc fluoride:
:2
PCl3 + 3
ZnF2 → 2 PF
3 + 3
ZnCl2
Biological activity
Phosphorus trifluoride is similar to
carbon monoxide
Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and 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 ...
in that it is a gas which strongly binds to
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
in
hemoglobin
Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...
, preventing the blood from absorbing oxygen.
Precautions
PF
3 is highly
toxic, comparable to
phosgene.
References
Further reading
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External links
National Pollutant Inventory - Fluoride and compounds fact sheetWebBook page for PF3
{{DEFAULTSORT:Phosphorus Trifluoride
Phosphorus fluorides
Phosphorus(III) compounds
Blood agents