A chemical compound is a pure chemical substance consisting of two or more different chemical e
Krypton difluoride, KrF
2, was the first
compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
of
kryptonKrypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...
discovered. It is a
volatileVolatility in the context of chemistry, physics and thermodynamics is a measure of the tendency of a substance to vaporize. It has also been defined as a measure of how readily a substance vaporizes...
, colourless solid. The structure of the KrF
2 molecule is linear, with Kr−F distances of 188.9 pm. It reacts with strong
Lewis acidA Lewis acid, A, is a chemical compound that can accept a pair of electrons from a Lewis base, B, that acts as an electron-pair donor, forming an adduct, AB:
A + :B → A—B...
s to form salts of the KrF
+ and Kr
2F
3+ cations.
Synthesis
Krypton difluoride can be synthesized using many different methods including electrical discharge, photochemical hot wire and proton bombardment.
It can also be prepared by irradiating krypton with ultraviolet rays in a fluorine-argon gas mixture at liquid helium temperature. The product can be stored at −78 °C without decomposition.
Electrical discharge
The first method used to make krypton difluoride and the only one ever reported to produce krypton tetrafluoride was the electrical discharge method. The electrical discharge method involves having 1:1 to 2:1 mixtures of F
2 to Kr at a pressure of 40 to 60 torr and then arcing large amounts of energy between it. Rates of almost 0.25 g/h can be achieved. The problem with this method is that it is unreliable with respect to yield.
Proton Bombardment
Using proton bombardment for the production of KrF
2 has a maximum production rate of about 1 g/h. This is achieved by bombarding mixtures of Kr and F
2 with a proton beam that is operating at an energy level of 10 MeV and at a temperature of about 133 K. It is a fast method of producing relatively large amounts of KrF
2, it runs into difficulties in that it requires a source of α-particles which usually would come from a cyclotron.
Photochemical
The photochemical process for the production of KrF
2 involves the use of UV light and can produce under ideal circumstances 1.22 g/h. The ideal wavelengths to use are in the range of 303-313 nm. It is important to note that harder UV radiation is detrimental to the production of KrF
2. In order to avoid the harder wavelengths, simply using Pyrex glass or Vycor or quartz will significantly increase yield because they all block harder UV light. In a series of experiments performed by S. A Kinkead et al., is was shown that a quartz insert (UV cut off of 170 nm) produced on average 158 mg/h, Vycor 7913 (UV cut off of 210 nm) produced on average 204 mg/h and Pyrex 7740 (UV cut off of 280 nm) produced on average 507 mg/h. It is clear from these results that higher energy ultra violet light reduces the yield significantly. The ideal circumstances for the production KrF
2 by a photochemical process appear to occur when krypton is a solid and fluorine is a liquid which occur at 77K. The biggest problem with this method is that is requires the handling of liquid F
2 and the potential of it being released if it becomes over pressurized.
Hot Wire
The hot wire method for the production of KrF
2 involves having the krypton in a solid state with a hot wire running a few centimeters away from it as fluorine gas is then run past the wire. The wire has a large current, causing it to reach temperatures around 680 °C. This causes the fluorine gas to split into its radicals which then can react with the solid krypton. Under ideal conditions, it has been known to reach a maximum yield of 6 g/h. In order to achieve optimal yields the gap between the wire and the solid krypton should be 1 cm, giving rise to a temperature gradient of about 900 °C/cm. The only major downside to this method is the amount of electricity that has to be passed through the wire thus making it dangerous if not properly set up.
Structure
Krypton difluoride can exist in one of two possible crystallographic morphologies: α-phase and β-phase. β-KrF
2 generally exists at above −80 °C, while the α-KrF
2 is more stable at lower temperatures. The unit cell of α-KrF
2 is body centred tetragonal.
Chemistry
Krypton difluoride is primarily a powerful oxidising and fluorinating agent. It can oxidise
goldGold is a chemical element with the symbol Au and an atomic number of 79. It has been a highly sought-after precious metal for coinage, jewelry, and other arts since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Gold is...
to its highest-known oxidation state, +5:
- 7 (g) + 2 Au (s) → 2 KrFAuF (s) + 5 Kr (g)
KrFAuF decomposes at 60°C into
gold(V) fluorideGold fluoride is a fluoride of gold where gold is in its highest known oxidation state. It is a red solid and is very corrosive. It is very reactive and unstable at room temperature, and liberates fluorine spontaneously...
and krypton and fluorine gases:
- KrFAuF → (s) + Kr (g) + (g)
can also directly oxidise
xenonXenon is a chemical element represented by the symbol Xe. Its atomic number is 54. A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
to
xenon hexafluorideXenon hexafluoride is a noble gas compound with the formula XeF6 and the highest of the three binary fluorides of xenon, the other two being XeF2 and XeF4. All are exergonic and stable at normal temperatures. XeF6 is the strongest fluorinating agent of...
:
- 3 + Xe → + 3 Kr
is used to synthesize the otherwise inaccessible BrF cation. reacts with to form the salt KrFSbF; the KrF cation is capable of oxidising both
{{chembox
| Name = Krypton difluoride
| ImageFile = Krypton-difluoride-2D-dimensions.png
| ImageName = Krypton difluoride
| ImageFile1 = Krypton-difluoride-3D-vdW.png
| ImageName1 = Krypton difluoride
| IUPACName = krypton(II) fluoride
| OtherNames = krypton difluoride, krypton fluoride
| Section1 = {{Chembox Identifiers
| CASNo = 13773-81-4
| RTECS =
}}
| Section2 = {{Chembox Properties
| Formula = KrF2
| MolarMass = 121.7968 g/mol
| Appearance = colourless solid
| Density = 3.24 g/cm3 solid
| Solubility = reacts
| SolubleOther = slightly soluble in liquid fluorineFluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F
2 molecule. F
2 is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the...
| MeltingPt =
| BoilingPt = 25 °C (decomposes)
}}
| Section3 = {{Chembox Structure
| MolShape = linear
| CrystalStruct = Body Centred Tetragonal
| Dipole = 0
DThe debye is a CGS unit of electric dipole moment
[Electric dipole moment is defined as charge times displacement:] Historically the debye was defined as the dipole moment resulting from two charges of opposite sign but an equal magnitude of 10
-10 statcoulomb
}}
| Section7 = {{Chembox Hazards
| MainHazards =
| FlashPt =
| RPhrases =
| SPhrases =
}}
| Section8 = {{Chembox Related
| OtherCpds = KrF4; KrO; Kr(OTeF5)2; XeF2Xenon difluoride is a powerful fluorinating agent with the chemical formula , and one of the most stable xenon compounds. Like most covalent inorganic fluorides it is moisture sensitive. It decomposes on contact with light or water vapour. Xenon difluoride is a dense, white crystalline solid. It...
}}
}}
{{seealso|Krypton fluoride laser}}
Krypton difluoride, KrF2, was the first compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
of kryptonKrypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...
discovered. It is a volatileVolatility in the context of chemistry, physics and thermodynamics is a measure of the tendency of a substance to vaporize. It has also been defined as a measure of how readily a substance vaporizes...
, colourless solid. The structure of the KrF2 molecule is linear, with Kr−F distances of 188.9 pm. It reacts with strong Lewis acidA Lewis acid, A, is a chemical compound that can accept a pair of electrons from a Lewis base, B, that acts as an electron-pair donor, forming an adduct, AB:
A + :B → A—B...
s to form salts of the KrF+ and Kr2F3+ cations.
Synthesis
Krypton difluoride can be synthesized using many different methods including electrical discharge, photochemical hot wire and proton bombardment.
It can also be prepared by irradiating krypton with ultraviolet rays in a fluorine-argon gas mixture at liquid helium temperature. The product can be stored at −78 °C without decomposition.
Electrical discharge
The first method used to make krypton difluoride and the only one ever reported to produce krypton tetrafluoride was the electrical discharge method. The electrical discharge method involves having 1:1 to 2:1 mixtures of F2 to Kr at a pressure of 40 to 60 torr and then arcing large amounts of energy between it. Rates of almost 0.25 g/h can be achieved. The problem with this method is that it is unreliable with respect to yield.
Proton Bombardment
Using proton bombardment for the production of KrF2 has a maximum production rate of about 1 g/h. This is achieved by bombarding mixtures of Kr and F2 with a proton beam that is operating at an energy level of 10 MeV and at a temperature of about 133 K. It is a fast method of producing relatively large amounts of KrF2, it runs into difficulties in that it requires a source of α-particles which usually would come from a cyclotron.
Photochemical
The photochemical process for the production of KrF2 involves the use of UV light and can produce under ideal circumstances 1.22 g/h. The ideal wavelengths to use are in the range of 303-313 nm. It is important to note that harder UV radiation is detrimental to the production of KrF2. In order to avoid the harder wavelengths, simply using Pyrex glass or Vycor or quartz will significantly increase yield because they all block harder UV light. In a series of experiments performed by S. A Kinkead et al., is was shown that a quartz insert (UV cut off of 170 nm) produced on average 158 mg/h, Vycor 7913 (UV cut off of 210 nm) produced on average 204 mg/h and Pyrex 7740 (UV cut off of 280 nm) produced on average 507 mg/h. It is clear from these results that higher energy ultra violet light reduces the yield significantly. The ideal circumstances for the production KrF2 by a photochemical process appear to occur when krypton is a solid and fluorine is a liquid which occur at 77K. The biggest problem with this method is that is requires the handling of liquid F2 and the potential of it being released if it becomes over pressurized.
Hot Wire
The hot wire method for the production of KrF2 involves having the krypton in a solid state with a hot wire running a few centimeters away from it as fluorine gas is then run past the wire. The wire has a large current, causing it to reach temperatures around 680 °C. This causes the fluorine gas to split into its radicals which then can react with the solid krypton. Under ideal conditions, it has been known to reach a maximum yield of 6 g/h. In order to achieve optimal yields the gap between the wire and the solid krypton should be 1 cm, giving rise to a temperature gradient of about 900 °C/cm. The only major downside to this method is the amount of electricity that has to be passed through the wire thus making it dangerous if not properly set up.
Structure
Krypton difluoride can exist in one of two possible crystallographic morphologies: α-phase and β-phase. β-KrF2 generally exists at above −80 °C, while the α-KrF2 is more stable at lower temperatures. The unit cell of α-KrF2 is body centred tetragonal.
Chemistry
Krypton difluoride is primarily a powerful oxidising and fluorinating agent. It can oxidise goldGold is a chemical element with the symbol Au and an atomic number of 79. It has been a highly sought-after precious metal for coinage, jewelry, and other arts since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Gold is...
to its highest-known oxidation state, +5:
- 7 {{chem|KrF|2}} (g) + 2 Au (s) → 2 KrF{{su|p=+}}AuF{{su|b=6|p=−}} (s) + 5 Kr (g)
KrF{{su|p=+}}AuF{{su|b=6|p=−}} decomposes at 60°C into gold(V) fluorideGold fluoride is a fluoride of gold where gold is in its highest known oxidation state. It is a red solid and is very corrosive. It is very reactive and unstable at room temperature, and liberates fluorine spontaneously...
and krypton and fluorine gases:
- KrF{{su|p=+}}AuF{{su|b=6|p=−}} → {{chem|AuF|5}} (s) + Kr (g) + {{chem|F|2}} (g)
{{chem|KrF|2}} can also directly oxidise xenonXenon is a chemical element represented by the symbol Xe. Its atomic number is 54. A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
to xenon hexafluorideXenon hexafluoride is a noble gas compound with the formula XeF6 and the highest of the three binary fluorides of xenon, the other two being XeF2 and XeF4. All are exergonic and stable at normal temperatures. XeF6 is the strongest fluorinating agent of...
:
- 3 {{chem|KrF|2}} + Xe → {{chem|XeF|6}} + 3 Kr
{{chem|KrF|2}} is used to synthesize the otherwise inaccessible BrF{{su|b=6|p=+}} cation. {{chem|KrF|2}} reacts with {{chem|SbF|5}} to form the salt KrF{{su|p=+}}SbF{{su|b=6|p=−}}; the KrF{{su|p=+}} cation is capable of oxidising both
{{chembox
| Name = Krypton difluoride
| ImageFile = Krypton-difluoride-2D-dimensions.png
| ImageName = Krypton difluoride
| ImageFile1 = Krypton-difluoride-3D-vdW.png
| ImageName1 = Krypton difluoride
| IUPACName = krypton(II) fluoride
| OtherNames = krypton difluoride, krypton fluoride
| Section1 = {{Chembox Identifiers
| CASNo = 13773-81-4
| RTECS =
}}
| Section2 = {{Chembox Properties
| Formula = KrF2
| MolarMass = 121.7968 g/mol
| Appearance = colourless solid
| Density = 3.24 g/cm3 solid
| Solubility = reacts
| SolubleOther = slightly soluble in liquid fluorineFluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F
2 molecule. F
2 is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the...
| MeltingPt =
| BoilingPt = 25 °C (decomposes)
}}
| Section3 = {{Chembox Structure
| MolShape = linear
| CrystalStruct = Body Centred Tetragonal
| Dipole = 0 DThe debye is a CGS unit of electric dipole moment
[Electric dipole moment is defined as charge times displacement:] Historically the debye was defined as the dipole moment resulting from two charges of opposite sign but an equal magnitude of 10
-10 statcoulomb
}}
| Section7 = {{Chembox Hazards
| MainHazards =
| FlashPt =
| RPhrases =
| SPhrases =
}}
| Section8 = {{Chembox Related
| OtherCpds = KrF4; KrO; Kr(OTeF5)2; XeF2Xenon difluoride is a powerful fluorinating agent with the chemical formula , and one of the most stable xenon compounds. Like most covalent inorganic fluorides it is moisture sensitive. It decomposes on contact with light or water vapour. Xenon difluoride is a dense, white crystalline solid. It...
}}
}}
{{seealso|Krypton fluoride laser}}
Krypton difluoride, KrF2, was the first compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
of kryptonKrypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...
discovered. It is a volatileVolatility in the context of chemistry, physics and thermodynamics is a measure of the tendency of a substance to vaporize. It has also been defined as a measure of how readily a substance vaporizes...
, colourless solid. The structure of the KrF2 molecule is linear, with Kr−F distances of 188.9 pm. It reacts with strong Lewis acidA Lewis acid, A, is a chemical compound that can accept a pair of electrons from a Lewis base, B, that acts as an electron-pair donor, forming an adduct, AB:
A + :B → A—B...
s to form salts of the KrF+ and Kr2F3+ cations.
Synthesis
Krypton difluoride can be synthesized using many different methods including electrical discharge, photochemical hot wire and proton bombardment.
It can also be prepared by irradiating krypton with ultraviolet rays in a fluorine-argon gas mixture at liquid helium temperature. The product can be stored at −78 °C without decomposition.
Electrical discharge
The first method used to make krypton difluoride and the only one ever reported to produce krypton tetrafluoride was the electrical discharge method. The electrical discharge method involves having 1:1 to 2:1 mixtures of F2 to Kr at a pressure of 40 to 60 torr and then arcing large amounts of energy between it. Rates of almost 0.25 g/h can be achieved. The problem with this method is that it is unreliable with respect to yield.
Proton Bombardment
Using proton bombardment for the production of KrF2 has a maximum production rate of about 1 g/h. This is achieved by bombarding mixtures of Kr and F2 with a proton beam that is operating at an energy level of 10 MeV and at a temperature of about 133 K. It is a fast method of producing relatively large amounts of KrF2, it runs into difficulties in that it requires a source of α-particles which usually would come from a cyclotron.
Photochemical
The photochemical process for the production of KrF2 involves the use of UV light and can produce under ideal circumstances 1.22 g/h. The ideal wavelengths to use are in the range of 303-313 nm. It is important to note that harder UV radiation is detrimental to the production of KrF2. In order to avoid the harder wavelengths, simply using Pyrex glass or Vycor or quartz will significantly increase yield because they all block harder UV light. In a series of experiments performed by S. A Kinkead et al., is was shown that a quartz insert (UV cut off of 170 nm) produced on average 158 mg/h, Vycor 7913 (UV cut off of 210 nm) produced on average 204 mg/h and Pyrex 7740 (UV cut off of 280 nm) produced on average 507 mg/h. It is clear from these results that higher energy ultra violet light reduces the yield significantly. The ideal circumstances for the production KrF2 by a photochemical process appear to occur when krypton is a solid and fluorine is a liquid which occur at 77K. The biggest problem with this method is that is requires the handling of liquid F2 and the potential of it being released if it becomes over pressurized.
Hot Wire
The hot wire method for the production of KrF2 involves having the krypton in a solid state with a hot wire running a few centimeters away from it as fluorine gas is then run past the wire. The wire has a large current, causing it to reach temperatures around 680 °C. This causes the fluorine gas to split into its radicals which then can react with the solid krypton. Under ideal conditions, it has been known to reach a maximum yield of 6 g/h. In order to achieve optimal yields the gap between the wire and the solid krypton should be 1 cm, giving rise to a temperature gradient of about 900 °C/cm. The only major downside to this method is the amount of electricity that has to be passed through the wire thus making it dangerous if not properly set up.
Structure
Krypton difluoride can exist in one of two possible crystallographic morphologies: α-phase and β-phase. β-KrF2 generally exists at above −80 °C, while the α-KrF2 is more stable at lower temperatures. The unit cell of α-KrF2 is body centred tetragonal.
Chemistry
Krypton difluoride is primarily a powerful oxidising and fluorinating agent. It can oxidise goldGold is a chemical element with the symbol Au and an atomic number of 79. It has been a highly sought-after precious metal for coinage, jewelry, and other arts since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Gold is...
to its highest-known oxidation state, +5:
- 7 {{chem|KrF|2}} (g) + 2 Au (s) → 2 KrF{{su|p=+}}AuF{{su|b=6|p=−}} (s) + 5 Kr (g)
KrF{{su|p=+}}AuF{{su|b=6|p=−}} decomposes at 60°C into gold(V) fluorideGold fluoride is a fluoride of gold where gold is in its highest known oxidation state. It is a red solid and is very corrosive. It is very reactive and unstable at room temperature, and liberates fluorine spontaneously...
and krypton and fluorine gases:
- KrF{{su|p=+}}AuF{{su|b=6|p=−}} → {{chem|AuF|5}} (s) + Kr (g) + {{chem|F|2}} (g)
{{chem|KrF|2}} can also directly oxidise xenonXenon is a chemical element represented by the symbol Xe. Its atomic number is 54. A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
to xenon hexafluorideXenon hexafluoride is a noble gas compound with the formula XeF6 and the highest of the three binary fluorides of xenon, the other two being XeF2 and XeF4. All are exergonic and stable at normal temperatures. XeF6 is the strongest fluorinating agent of...
:
- 3 {{chem|KrF|2}} + Xe → {{chem|XeF|6}} + 3 Kr
{{chem|KrF|2}} is used to synthesize the otherwise inaccessible BrF{{su|b=6|p=+}} cation. {{chem|KrF|2}} reacts with {{chem|SbF|5}} to form the salt KrF{{su|p=+}}SbF{{su|b=6|p=−}}; the KrF{{su|p=+}} cation is capable of oxidising both {{chemBromine pentafluoride, BrF5, is an interhalogen compound and a fluoride of bromine. It is a strong fluorination reagent.It melts at −61.30 °C and boils at 40.25 °C. BrF5 finds use in oxygen isotope analysis. Laser ablation of solid silicates in the presence of bromine...
and {{chemChlorine pentafluoride has formula ClF5. It was first synthesized in 1963.Its square pyramidal structure with C4v symmetry was confirmed by its high resolution19F NMR spectrum.-Preparation:...
to BrF{{su|b=6|p=+}} and ClF{{su|b=6|p=+}}, respectively.
External links