# Monofluorophosphate

Monofluorophosphate is an anion with the formula PO$_3$F$^{2−}$, which is a phosphate group with one oxygen atom substituted with a fluoride atom. The charge of the ion is −2. The ion resembles sulfate in size, shape and charge, and can thus form compounds with the same structure as sulfates. These include Tutton's salts and langbeinites. The most well-known compound of monofluorophosphate is sodium monofluorophosphate, commonly used in toothpaste.
Related ions include difluorophosphate (PO$_2$F−2) and hexafluorophosphate ([PF$_6$]$^−$). The related neutral molecule is phosphenic fluoride PO$_2$F.
Organic derivatives can be highly toxic and include diisopropyl fluorophosphate. Some of the Novichok agents are monofluorophosphate esters. Names are given to these by naming the groups attached as esters and then adding "fluorophosphonate" to the end of the name. Two organic groups can be attached. Other related nerve gas substances may not be esters, and instead have carbon-phosphorus or nitrogen-phosphorus bonds. The organic fluorophosphonates react with serine esterases and serine proteases irreversibly. This prevents these enzymes from functioning. Such an important enzyme is acetylcholinesterase as found in most animals. Some of the organic esters are detoxified in mammals by an enzyme in the blood and liver called paraoxonase PON1.
Willy Lange from Berlin discovered sodium monofluorophosphate in 1929. He fruitlessly tried to make monofluorophosphoric acid. However, he did discover the highly toxic organic esters. Following this discovery various nerve gases like sarin were developed.
Fluorophosphate glasses are low melting point kinds of glass which are mixtures of fluoride and phosphate metal compounds. For example, the composition 10% SnO, 40% SnF$_2$, 50% P$_2$O$_5$ forms a glass melting about 139 °C. PbO and PbF$_2$ can lower the melting temperature, and increase water resistance. These glasses can also be coloured by various other elements, and organic dyes.
Some mixed anion compounds are known with other anions like fluoride, chloride, difluorophosphate or tetrafluoroborate.

## Production

Hydrolysis of difluorophosphate with an alkali produces monofluorophosphate.
    PO$_2$F−2 + 2 MOH → M$_2$PO$_3$F + H$_2$O + F$^−$
Industrial production is by reaction of a fluoride with a metaphosphate.
    MF + MPO$_3$ → M$_2$PO$_3$F
Disodium hydrogen phosphate or tetrasodium pyrophosphate can react with hydrogen fluoride to form the sodium salt.
    Na$_2$HPO$_4$ or Na$_4$P$_2$O$_7$
Phosphoric acid reacts with metal fluorides dissolved in molten urea to yield monofluorophosphates.

## Properties

Monofluorophosphates are stable at room temperature, but will decompose when heated. For example, at 450 K (177 °C), silver monofluorophosphate gives off phosphoryl fluoride (POF$_3$) as a gas leaving behind silver phosphate (Ag$_3$PO$_4$) and silver pyrophosphate (Ag$_4$P$_2$O$_7$).
In inorganic compounds the monofluorophosphate ion has an average P–O bond length of 1.51 Å. The P–F bond is longer, on average 1.58 Å. The O P F angle is 104.8°, smaller than the tetrahedral 109.47°. To compensate the O P O bond angle is 113.7° on average.
Most commonly the monofluorophosphtae ion takes on point group 1, but a significant number have point group m. Only two are known with 3m and one with 3.
When compared to sulfates, some are isotypical with the monofluorophosphates. Yet others have sulfates that take on a different form. But most know monofluorophosphates have no known equivalent sulfate.

## Compounds

| Name | Formula | Crystal form | Formula weight | Density | Comment | ChemSpider | PubChem | CAS |
| fluorophosphoric acid | H$_2$PO$_3$F | | 99.986 | | | 22687 | 24267 | 13537-32-1 |
| | BePO$_3$F-I | Pc a=4.9331 b=6.6283 c=4.7083 β=90.2007 Z=2 | | | band gap 8.03 eV SHG 1.72×KDP | | | |
| | BePO$_3$F-II | P6$_3$ a=4.9651 c=9.3236 Z=2 | | | | | | |
| | BePO$_3$F-III | Cc a=4.9542 b=8.5812 c=10.0532 β=98.0674 Z=4 | | | | | | |
| | BePO$_3$F-IV | Cc a=8.5892 b=4.9532 c=10.1526 β=92.4967 Z=4 | | | | | | |
| | BePO$_3$F-V | Cm a=9.2837 b=5.1602 c=7.1809 β=143.9321 Z=2 | | | | | | |
| | BePO$_3$F-VI | P6$_3$mc a=5.1519 c=8.8598 Z=2 | | | | | | |
| ammonium monofluorophosphate | (NH$_4$)$_2$PO$_3$F | orthorhombic: a = 6.29 Å, b = 8.31 Å, c = 12.70 Å, β = 99.6°, Z = 4 | 134.05 | 1.633 | | 8324505 | | |
| ammonium monofluorophosphate hydrate | (NH$_4$)$_2$PO$_3$F·H$_2$O | monoclinic: a = 7.9481 Å, b = 11.3472 Å, c = 6.0425 Å, β = 117.55°, Z = 4 monoclinic: a = 6.3042 Å, b = 8.2942 Å, c = 12.760 Å, β = 98.415°, Z = 4, V = 657.416 Å$^3$ | 152.05 | 1.536 | | | | |
| ammonium tetrafluoroborate-monofluorophosphate | (NH$_4$)$_3$[PO$_3$F][BF$_4$] | monoclinic P2$_1$/m: a = 7.8384 Å, b = 6.0996 Å, c = 9.9079 Å, β = 111.990°, V = 439.24 Å$^3$, Z = 2 | 238.91 | 1.806 | | | | |
| | (NH$_4$)$_2$PO$_3$F·NH$_4$NO$_3$ | monoclinic P2$_1$/n a=10.3145 b=6.1034 c=14.3299 β=103.885° Z=4 | 875.8 | 1.624 | @−73 | | | |
| | (NH$_4$)$_2$PO$_3$F·NH$_4$NO$_3$ | triclinic P1a=10.3414 b=6.1056 c=14.1704 α=91.248 β=101.016 γ=89.173 Z=4 | 877.98 | 1.620 | @−98 | | | |
| | (NH$_4$)$_2$PO$_3$F·NH$_4$NO$_3$ | monoclinic P2$_1$ppa=10.3182 b=6.0591 c=14.3715 β=98.563 Z=4 | 888.48 | 1.601 | @−173 | | | |
| | (N$_2$H$_6$)[HPO$_3$F]$_2$ | monoclinic C12/c1 a=14.1326 b=7.0340 c=7.9877 β=96.763 Z=4 | 788.52 | 1.954 | colourless; large birefringence | | | |
| sodium monofluorophosphate | Na$_2$PO$_3$F | | | | | 22686 | 24266 | 10163-15-2 |
| sodium hydrogen monofluorophosphate | NaHPO$_3$F | | 121.968 | | | | 19860808 | 20859-36-3 |
| sodium hydrogen monofluorophosphate dihydrate | NaHPO$_3$F·2H$_2$O | monoclinic: a = 19.112 Å, b = 5.341 Å, c = 12.72 Å, α = 110.18°, V = 1219.4 Å$^3$ | 167.01 | 1.819 | | | | |
| magnesium monofluorophosphate | MgPO$_3$F | | 122.28 | | | | 23206079 | |
| diammonium manganese dimonofluorophosphate dihydrate | (NH$_4$)$_2$Mg(PO$_3$F)$_2$·2H$_2$O | monoclinic C2/m: a = 13.374 Å, b = 5.3541 Å, c = 7.385 Å, β = 113.758°, V = 484.01 Å$^3$, Z = 2 | 292.37 | 2.006 | | | | |
| potassium monofluorophosphate | K$_2$PO$_3$F | orthorhombic: a = 7.554 Å, b = 5.954 Å, c = 10.171 Å, V = 457 Å$^3$, Z = 4 (at 20 °C) | 176.17 | 2.57 | | | | 20859-37-4 14306-73-1 |
| | K$_2$PO$_3$F·KF | | | | | | | |
| Potassium hydrogen monofluorophosphate | KHPO$_3$F | monoclinic: a = 7.273 Å, b = 14.086 Å, c = 7.655 Å, β = 90.13°, Z = 8, V = 784.233 Å$^3$ | | | | | | |
| Tripotassium hydrogen monofluorophosphate | K$_3$H(PO$_3$F)$_2$ | monoclinic: a = 7.973 Å; b = 11.635 Å; c = 9.668 Å, β = 113.52°, Z = 4, V = 822.35 Å$^3$ | | | | | | |
| Ammonium dipotassium hydrogen difluorophosphate | NH$_4$K$_2$H(PO$_3$F)$_2$ | | | | | | | |
| calcium monofluorophosphate dihydrate | CaPO$_3$F·2H$_2$O | triclinic: a = 8.6497 Å, b = 6.4614 Å, c = 5.7353 Å, α = 119.003°, β = 110.853°, γ = 94.146°, V = 249.943 Å$^3$, Z = 2 | | 2.313 | | 8096036 | 9920401 | 37809-19-1 |
| calcium monofluorophosphate hemihydrate | CaPO$_3$F·0.5H$_2$O | | | | | | | |
| vanadium monofluorophosphate | VPO$_3$F | | 148.91 | | | | 20452625 | |
| chromium(III) monofluorophosphate | Cr$_2$(PO$_3$F)$_3$·18.8H$_2$O | triclinic: a = 11.594 Å, b = 15.292 Å, c = 15.360 Å, α = 83.804°, β = 84.203, γ = 82.597, V = 2674.1 Å$^3$, Z = 4 | 736.88 | 1.830 | | | | |
| ammonium chromium(III) difluorophosphate hexahydrate | NH$_4$Cr(PO$_3$F)$_2$·6H$_2$O | R3$_m$: a = 6.5491 Å, c = 25.438 Å, Z = 3 | 9.4489 | 1.972 | green | | | |
| manganese(II) fluorophosphate dihydrate | MnPO$_3$F·2H$_2$O | triclinic: a = 5.528 Å, b = 5.636 Å, c = 8.257 Å, α = 81.279°, β = 75.156°, γ = 71.722°, Z = 2 | 188.94 | | | | | |
| diammonium manganese monofluorophosphate | (NH$_4$)$_2$Mn(PO$_3$F)$_2$·2H$_2$O | monoclinic: P2$_1$/n a = 12.558 Å, b = 5.5456 Å, c = 7.422 Å, β = 99.918°, Z = 2 | 500.9 | 2.142 | pink | | | |
| ammonium trimanganese dimonofluorophosphate difluorophosphate difluoride | (NH$_4$)Mn$_3$(PO$_3$F)$_2$(PO$_2$F$_2$)F$_2$ | monoclinic: a = 20.3151 Å, b = 7.6382 Å, c = 7.8312 Å, β = 103.589°, V = 1181.16 Å$^3$ | 517.8 | 2.9116 | | | | |
| diammonium cobalt dimonofluorophosphate dihydrate | (NH$_4$)$_2$Co(PO$_3$F)$_2$·2H$_2$O | monoclinic C2/m: a = 13.386 Å, b = 5.3476 Å, c = 7.390 Å, β = 114.02°, V = 483.2 Å$^3$, Z = 2 | 326.99 | 2.247 | | | | |
| ammonium tricobalt dimonofluorophosphate difluorophosphate difluoride | (NH$_4$)Co$_3$(PO$_3$F)$_2$(PO$_2$F$_2$)F$_2$ | monclinic: a = 19.9678 Å, b = 7.4883 Å, c = 7.5679 Å, β = 102.676°, V = 1104.01 Å$^3$ | 529.7 | 3.1871 | | | | |
| Diammonium nickel dimonofluorophosphate hexahydrate | (NH$_4$)$_2$Ni(PO$_3$F)$_2$·6H$_2$O | monoclinic: a = 6.2700 Å, b = 12.2845 Å, c = 9.1894 Å, β = 106.033°, Z = 2 | 680.27 | 1.947 | blue Tutton | | | |
| copper monofluorophosphate | CuPO$_3$F·5H$_2$O | | 251.59 | | | | | |
| basic copper potassium monofluorophosphate | Cu$_2$K(OH)(PO$_3$F)$_2$·5H$_2$O | monoclinic: a = 9.094 Å, b = 6.333 Å, c = 7.75 Å, β = 117.55°, Z = 2 | | | natrochalcite | | | |
| diammonium diaquabis(monofluorophosphato) copper | Cu(NH$_4$)$_2$(PO$_3$F)$_2$·2H$_2$O | monoclinic: a = 13.454 Å, b = 5.243 Å, c = 7.518 Å, β = 114.59°, V = 482.2 Å$^3$, Z = 2 | 331.6 | 2.28 | | | | |
| basic tetraammonium dicopper dimonofluorophosphate | NH$_4$Cu$_2$OH(PO$_3$F)$_2$·H$_2$O | C2/m: a = 9.1012 Å, b = 6.4121 Å, c = 7.8506 Å, β = 116.277°, Z = 2 | 410.80 | 3.040 | light blue natrochalcite | | | |
| zinc monofluorophosphate | ZnPO$_3$F·2.5H$_2$O | triclinic: a = 7.6020 Å, b = 7.6490 Å, c = 9.4671 Å, α = 88.633°, β = 88.888°, γ = 87.182°, V = 549.58 Å$^3$, Z = 4 | 163.35 | 2.518 | | | 20846323 | 68705-59-9 |
| anhydrous diammonium zinc tetramonofluorophosphate | (NH$_4$)$_2$Zn$_3$(PO$_3$F)$_4$ | cubic: a = 11.4769 Å | | | | | | |
| diammonium zinc dimonofluorophosphate | (NH$_4$)$_2$Zn(PO$_3$F)$_2$·0.2H$_2$O | monoclinic C2/c: a = 18.936 Å, b = 7.6955 Å, c = 20.528 Å, β = 108.641° Z = 12 | 2834.4 | 2.117 | colourless | | | |
| diammonium trizinc tetramonofluorophosphate | (NH$_4$)$_2$Zn$_3$(PO$_3$F)$_4$·H$_2$O | cubic I4$_3$d: a = 11.3693 Å, Z = 4 | 1469.6 | 2.902 | colourless | | | |
| rubidium monofluorophosphate | Rb$_2$PO$_3$F | orthorhombic: a = 7.8714 Å, b = 6.1236 Å, c = 10.5424 Å, V = 508.15 Å$^3$, Z = 4 (at 17 °C) | 268.9 | 3.514 | | | | |
| Rubidium hydrogen monofluorophosphate | RbHPO$_3$F | monoclinic: a = 7.465 Å, b = 15.551 Å, c = 7.563 Å, β = 105.38°, V = 846.533 Å$^3$, Z = 8 | | | | | | |
| | Na$_{1.5}$Rb$_{0.5}$PO$_3$F·H$_2$O | orthorhombic Pmn2$_1$: a = 6.015 Å, b = 8.965 Å, c = 4.9689 Å, Z = 2 | 267.97 | 2.398 | colourless | | | |
| strontium monofluorophosphate | SrPO$_3$F | monoclinic | 185.59 | | | | 18183579 | |
| strontium monofluorphosphate hydrate | SrPO$_3$F·H$_2$O | | 185.59 | | | | | |
| silver monofluorophosphate | Ag$_2$PO$_3$F | monoclinic: a = 9.245 Å, b = 5.585 Å, c = 14.784 Å, β = 90.178°, Z = 8 | 313.7 | | | | 44135907 | |
| trisilver ammonium monofluorophosphate | NH$_4$Ag$_3$(PO$_3$F)$_2$ | monoclinic: a = 30.895 Å, b = 5.5976 Å, c = 9.7522 Å, β = 90.027°, V = 1686.6 Å$^3$, Z = 8 | 537.59 | 4.234 | | | | |
| cadmium monofluorophosphate | CdPO$_3$F·2H$_2$O | triclinic P1_: a = 5.2678 Å, b = 6.6697 Å, c = 7.7037 Å, α = 65.506°, β = 85.919°, γ = 75.394°, V = 238.584 Å$^3$, Z = 2 | 246.40 | 3.430 | | | | |
| cadmium ammonium monofluorophosphate chloride dihydrate | Cd$_{2.5}$(NH$_4$)$_2$(PO$_3$F)$_3$Cl·2H$_2$O | | | | colourless | | | |
| tin monofluorophosphate | SnPO$_3$F·2.5H$_2$O | monoclinic | 216.68 | | | | 44717639 | 52262-58-5 |
| caesium monofluorophosphate | Cs$_2$PO$_3$F | orthorhombic: a = 8.308 Å, b = 6.3812 Å, c = 11.036 Å, V = 585.1 Å$^3$, Z = 4 (at −33 °C) | 363.8 | 4.129 | | | | |
| caesium hydrogen monofluorophosphate | CsHPO$_3$F | monoclinic: a = 14.478 Å, b = 5.929 Å, c = 5.413 Å, β = 103.30°, V = 452.2 Å$^3$, Z = 4 | 231.89 | | | | | |
| tricaesium diammonium hydrogen monofluorophosphate | Cs$_3$(NH$_4$)$_2$H$_3$(PO$_3$F)$_4$ | monoclinic: a = 20.619 Å, b = 12.076 Å, c = 15.856 Å, β = 102.58°, V = 3853 Å$^3$, Z = 8 | 829.72 | | | | | |
| barium monofluorophosphate | BaPO$_3$F | monoclinic: a = 11.3105 Å, b = 8.6934 Å, c = 9.2231 Å, β = 127.819°, Z = 4 orthorhombic | 235.299 | | | | 20836124 | 15600-53-0 |
| Mercurous monofluorophosphate | Hg$_2$PO$_3$F | orthorhombic: a = 9.406 Å, b = 12.145 Å, c = 8.567 Å, V = 978.7 Å$^3$, Z = 8 | | | | | | |
| lead monofluorophosphate | PbPO$_3$F | orthorhombic: a = 6.95 Å, b = 8.52 Å, c = 5.47 Å | | 6.24 | | | | |
| dilead monofluorophosphate dichloride hydrate | Pb$_2$(PO$_3$F)Cl$_2$·H$_2$O | orthorhombic Pnma: a = 20.486 Å, b = 5.3967 Å, c = 6.9722 Å, V = 770.8 Å$^3$, Z = 4 | 601.27 | 5.181 | | | | |
| ditheylammonium hydrogen monofluorophosphate | [NH$_2$(CH$_2$CH$_3$)$_2$]HPO$_3$F | orthorhombic: a = 12.892 Å, b = 9.530 Å, c = 13.555 Å, α = 90°, V = 1665 Å$^3$ | 173.12 | 1.381 | | | | |
| tetramethylammonium monofluorophosphate | [N(CH$_3$)$_4$]$_2$PO$_3$F | | 246.26 | | | | | |
| tetraethylammonium monofluorophosphate | [N(CH$_2$CH$_3$)$_4$]$_2$PO$_3$F | | 358.47 | | | | | |
| tetrabutylammonium monofluorophosphate | [N(CH$_2$CH$_2$CH$_2$CH$_3$)$_4$]$_2$PO$_3$F | | 582.90 | | | | | |
| piperazinium hydrogen monofluorophosphate | [PipzH$_2$]HPO$_3$F | monoclinic: a = 6.020 Å, b = 13.012 Å, c = 7.285 Å, α = 95.09°, V = 568.4 Å$^3$ | 286.11 | 1.672 | | | | |
| glutamine monofluorophosphate monohydrate | C$_5$H$_{12}$N$_2$O$_3$PFO$_3$ | | 246.131 | | | | 19989732 | |
| glutamine monofluorophosphate disodium dichloride | C$_{10}$H$_{20}$Cl$_2$FN$_4$Na$_2$O$_9$P | | 507.146 | | | 143826 | 164002 | |
| anilinium hydrogen monofluorophosphate | [C$_6$H$_8$N]$^+$[HPO$_3$F]$^−$ | monoclinic: a = 9.418 Å, b = 14.31 Å, c = 6.303 Å, β = 92.45°, V = 859 Å$^3$, Z = 4 | 193.12 | 1.51 | | | | |
| Tris(2-carbamoylguanidinium) hydrogen fluorophosphonate fluorophosphonate monohydrate | [C$_2$H$_7$N$_4$O$^+$]$_3$[HPO$_3$F]$^−$[PO$_3$F]$^{2−}$·H$_2$O | triclinic: a = 6.7523 Å, b = 8.2926 Å, c = 9.7297 Å, α = 100.630°, β = 90.885°, γ = 99.168°, V = 528.05 Å$^3$ | | | | | | |
| bis(2-carbamoylguanidinium) fluorophosphonate dihydrate | [C$_2$H$_7$N$_4$O$^+$]$_2$[PO$_3$F]$^{2−}$·2H$_2$O | | | | | | | |

### Organic

| Name | Formula | Formula weight | | ChemSpider | PubChem | CAS |
| dimethyl fluorophosphate | (CH$_3$)$_2$PO$_2$F | 128.039 | | 72304 | 80052 | 5954-50-7 |
| methyl ethyl fluorophosphate | (CH$_3$)(CH$_3$CH$_2$)PO$_2$F | | | | | |
| 1-[ethoxy(fluoro)phosphoryl]oxyethane | (CH$_3$CH$_2$)$_2$PO$_2$F | 156.093 | | | 67752 | 358-74-7 |
| isoflurophate | [(CH$_3$)$_2$CH]$_2$PO$_2$F | 184.147 | | 5723 | 5936 | 55-91-4 |
| 1-[fluoro(2-oxopropoxy)phosphoryl]oxypropan-2-one | | 212.113 | | | 129718773 | |
| isobutyl methyl fluorophosphate | | 170.12 | | | 129684440 | |
| 1-[fluoro(methoxy)phosphoryl]oxypentane | (CH$_3$)(CH$_3$CH$_2$CH$_2$CH$_2$CH$_2$)PO$_3$F | 184.147 | | | 129761096 | |
| 1-[fluoro(propoxy)phosphoryl]oxypropane | (CH$_3$CH$_2$CH$_2$)$_2$PO$_3$F | 184.147 | | 4954063 | 6451603 | 381-45-3 |
| O-isopropyl propyl fluorophosphonate | (CH$_3$)$_2$CH(CH$_3$CH$_2$CH$_2$)PO$_3$F | 184.147 | | | 88538036 | |
| O-1-methylbutyl ethyl fluorophosphonate | | 198.174 | | | 129761095 |
| dibutyl fluorophosphate | (CH$_3$CH$_2$CH$_2$CH$_2$)$_2$PO$_3$F | 212.201 | | 11640560 | 13025172 | 674-48-6 |
| di-sec-butyl fluorophosphate | [CH$_3$CH$_2$CH(CH$_3$)]$_2$PO$_3$F | 212.201 | | 92528 | 102452 | 625-17-2 |
| di(1,3-dimethyl-n-butyl) fluorophosphate | [(CH$_3$)$_2$CHCH$_2$CH(CH$_3$)]$_2$PO$_3$F | 268.309 | | 91838 | 101643 | 311-60-4 |
| 1-[fluoro(2-methylpentan-3-yloxy)phosphoryl]oxyoctane | | 296.363 | | | 129760905 | |
| methyl arachidonoyl fluorophosphonate | | 400.471 | | | 11741711 | 9916415 |
| 12-[fluoro(propan-2-yloxy)phosphoryl]oxydodec-1-ene | | 308.374 | | | 129892247 | |
| bis(4-phenylbutyl) fluorophosphate | (C$_6$H$_5$CH$_2$CH$_2$CH$_2$CH$_2$)$_2$PO$_3$F | 364.397 | | 162961 | 187452 | 85473-46-7 |
| 3′-fluoro-3′-deoxythymidine 5′-fluorophosphate | | 326.193 | | 2339398 | 3081896 | 152829-59-9 |
| cytidine 5′-fluorophosphate | | 325.189 | | | 87861929 | 68521-86-8 |
| chlorofluoromethylideneamino-2-chloroethyl fluorophosphate | ClFC=NClCH$_2$CH$_2$PO$_3$F | | A-230 Novichok agent | | |
| chlorofluoromethylideneamino-1-methyl-2-chloroethyl fluorophosphate | ClFC=NClCH$_2$CH(CH$_3$)PO$_3$F | | A-232 Novichok agent | | |
| chlorofluoromethylideneamino-1,2-dimethyl-2-chloroethyl fluorophosphate | ClFC=NCl(CH$_3$)CHCH(CH$_3$)PO$_3$F | | A-234 Novichok agent | | |

## Uses

Zinc monofluorophosphate can be used as a corrosion inhibitor for steel when salt is present.
Glutamine monofluorophosphate has been used as a fluoride-bearing medicine.