Difluorophosphate


Difluorophosphate or difluorodioxophosphate or phosphorodifluoridate is an anion with formula. It has a single negative charge and resembles perchlorate and monofluorosulfonate in shape and compounds. These ions are isoelectronic, along with tetrafluoroaluminate, phosphate, orthosilicate, and sulfate. It forms a series of compounds. The ion is toxic to mammals as it causes blockage to iodine uptake in the thyroid. However it is degraded in the body over several hours.
Compounds containing difluorophosphate may have it as a simple uninegative ion, it may function as a difluorophosphato ligand where it is covalently bound to one or two metal atoms, or go on to form a networked solid. It may be covalently bound to a non metal or an organic moiety to make an ester or an amide.

Formation

The ammonium salt of difluorophosphate is formed from treating phosphorus pentoxide with ammonium fluoride. This was how the ion was first made by its discoverer, Willy Lange, in 1929.
Alkali chlorides can react with dry difluorophosphoric acid to form alkali metal salts.
Fluoridation of dichlorophosphates can produce difluorophosphates. Another method is fluorination of phosphates or polyphosphates.
Trimethylsilyl difluorophosphate reacts with metal chlorides to give difluorophosphates.
The anhydride phosphoryl difluoride oxide reacts with oxides such as UO3 to yield difuorophosphates. Phosphoryl difluoride oxide also reacts with alkali fluorides to yield difluorophosphates.

Properties

In ammonium difluorophosphate the difluorophosphate ion has these interatomic dimensions: P–O length 1.457 Å, P–F length 1.541 Å, O–P–O angle 118.7°, F–P–O 109.4° and F–P–F angle 98.6°. Hydrogen bonding from ammonium to oxygen atoms causes a change to the difluorophosphate ion in the ammonium salt. In potassium difluorophosphate the ion has dimensions: P–O length 1.470 Å, P–F length 1.575 Å, O–P–O angle 122.4°, F–P–O 108.6° and F–P–F angle 97.1°.
On heating the salts that are not of alkali or alkaline earths, difluorophosphates decompose firstly by giving off POF3 forming a monofluorophosphate compound, and then this in turn decomposes to an orthophosphate compound.
Difluorophosphate salts are normally soluble and stable in water. However, in acidic or alkaline conditions they can be hydrolyzed to monofluorophosphates and hydrofluoric acid. The caesium and potassium salts are the least soluble.
Irradiating potassium difluorophosphate with gamma rays can make the free radicals PO2F•−, PO3F•− and.

Compounds

formulastructureinfraredmelting point °Creferencecomment
LiPO2F2360-
Be2>400dprepared from BeCl2 and acid
C2H5OPOF2-
NH4PO2F2Orthorhombic a=8·13, b=6·43, c=7·86 Å Z=4 space group PnmaP-F stretching 842 860 cm−1;P-O stretching 1138 1292 cm−1213-
NO2PO2F2515, 530, 550, 560, 575, 845, 880, 1145, 1300, 2390, 3760 cm−1nitronium formed from anydride and N2O5
NOPO2F2500, 840, 880, 1130, 1272, 1315, 2278 cm−1nitrosonium formed from anydride and N2O3
NaPO2F2210-
Mg2200-
Al31290 1200 971 918 642 582 541 505 cm−1 355Formed from AlEt3 and acid. Colourless insoluble powder. Polymeric.
Si4formed from SiCl4 and anhydride
Si3OPOF2formed from anhydride and 2O
KPO2F2Orthorhombic a=8.03 b=6.205 c=7.633 Å Z=4 V=380.9 Å3 density=2.44510, 525, 570, 835, 880, 1145, 1320, 1340 cm−1263colourless elongated prisms
Ca2•CH3COOCH2CH3-
Ca2>345d-
VO2PO2F2-
CrO22formed from anhydride;red-brown
Cr3320 385 490 575 905 955 1165 1255 cm−1formed from excess anhydride, green
Mn5PO2F2184-
HMn3dissolve manganese in acid; white
Mn32F2
Fe21290 1139 869 668 496 463 cm−1180dcolour blue green, hygroscopic, melts 250 °C, above 300 °C starts decomposing to Fe32
Fe31242 1173 965 914 570 528 493 262 cm−1>400decomposes at 230 °C yielding FeF3; dissolve iron in acid in presence of oxygen
KFe22F2
Co2173prepared from CoCl2 and acid; pink or blue; blue formed by heating pink to 140 °C
HCo3dissolve cobalt in acid; red-purple
Co2•2CH3CNmolw weight=342.9 orthorhombic a=9.227 Å b=13.871 Å c=9.471 Å V=1212 Å3 Z=4 density=1.88treat HCo3 with MeCN for a few weeks; red crystals
Co32F2
Ni2255dslowly prepared from NiCl2 and acid; yellow
HNi3dissolve nickel in acid; yellow
Cu2MW=265.5 orthorhombic Fddd a=10.134 Å b=24.49 Å c=34.06 Å Z=48 V=8454.3 Å3 density=2.50265dpale blue needles
CuI2monoclinic a=12.435 b=10.887 c=25.682 β=100.220 V=3421 Å3polymer colourless
Zn2?room tempglassy
ZnH24-
Ga3-
2380 492 520 551 616 709 750 899 949 1171 1218 1262 1295 1404 2922 2982dimer
RbPO2F2Orthorhombic a=8·15, b=6·45, c=7·79 Å Z=4 V=409.5 Å3 density=3.02P-F stretching 827 946 cm−1;P-O stretching 1145 1320 cm−1160white
Sr2250dprepared from SrCl2 and acid
Ag PO2F2-
Ag914-
Ag PO2F2-
Ag PO2F2Triclinic P1 a=7.687 b=10.740, c=13.568 Å, α=99.52°, β=96.83°, γ=99.83°, Z=2, V=1076 Å3mol weight=585.37 density 1.81
4,4'-Dicyanodiphenylacetylene AgPO2F2--
Cd2245d-
In31269 1179 962 910 567 528 492 269 cm−1white decomposes at 260 °C yielding InF3
2373 490 500 535 559 735 878 925 1128 1179 1275 1435 2928 3000dimer
SnCl22-
2Sn2204dprepared from 2SnCl2 and acid; yellow
2Sn2262dprepared from 2SnCl2 and acid; yellow
2Sn2245dprepared from 2SnCl2 and acid; yellow
2Sn2235dprepared from 2SnCl2 and acid; yellow
2Sn2114prepared from 2SnCl2 and acid; yellow
SbCl4PO2F2-
SbF4PO2F2-
2Re2PO2F2-
Bisgold Difluorophosphate-
IO2PO2F2Raman: 1163, 918 839, 799, 781, 737, 713, 637, 378, 329, 323, 295, 219, 191, 163, 130 cm−1yellowish colour, produced from IO3, decomposed by water
IO3PO2F2Raman: 1123, 891, 797, 717, 671, 643, 569, 473, 395, 367, 343, 305, 269, 247, 217 cm−1yellowish colour, produced from H5IO6, decomposed by water
FXePO2F2-
Xe2-
CsPO2F2Orthorhombic a=8·437, b=6·796, c=8·06 Å Z=4 V=462.1 Å3 density=3.36286-
Cs2Fe22F3-
Ba2>400-
Re5PO2F2-
Hg2-
Hg22Raman: 220 cm−1produced from anydride
TlPO2F2produced from andhydride, or acid on TlCl
2360 374 500 505 520 559 850 880 1120 1140 1195 1250 1285 2932 3020dimer
Pb2189d-
UO221124 980 924 854 498 260 cm−1IR spectrum due to UO22+
4NPO2F2-
1-ethyl-3-methylimidazolium difluorophosphateionic liquid
1-butyl-3-methylimidazolium difluorophosphateionic liquid
1-butyl-1-methylpyrrolidinium difluorophosphateionic liquid
1-butyl-1-methylpiperidinium difluorophosphateionic liquid
DidifluorophosphateTransitions to a metallic state below 137K
1,4-diphenyl-3,5-enanilo-4,5-dihydro-1,2,4-triazole monoclinic P21/n a=7.3811 b=14.9963 c=
16.922 β=102.138 V=1361.2 Z=4		insoluble; yellow-brown
Strychnine PO2F2-
Cocaine PO2F2-
Brucine PO2F2-
Morphine PO2F2-
N4 PO2F2-
HB4469 502 552 647 836 940 994 1093 1348 1567 cm−1formed from BBr3 and acid; liquid
LiB4monoclinic P21/c a=7.9074 Å b=14.00602 Å c=13.7851 Å β=121.913° Z=4479 502 568 833 945 1002 1080 1334 cm−1formed from HB4 and butyl lithium; colourless
HS2B4472 511 555 648 832 933 993 1082 1337 1436 2851 2921 3042 cm−1formed from BH3•S2 and acid; ionic liquid
3Al6trigonal R a=17.4058 Å b=17.4058 Å c=21.4947 Å γ=120° Z=6417 503 536 624 723 891 922 964 1174 1204 1283 cm−1formed from butyl lithium and triethyl aluminium and the acid; white
K2CrO24305 370 485 550 870 920 1050 1130 1250 cm−1formed from anhydride and K2CrO4; brown; dec 145°
Na2MoO24280 490 620 880 915 950 1020 1070 1140 1280 cm−1formed from anhydride and K2MoO4; white; dec 125 °C; amorphous
Na2WO24280 474 620 930 1030 1130 1230 cm−1formed from anhydride and K2WO4; white; dec 109 °C amorphous

Related substances

Difluorphosphoric acid

Difluorphosphoric acid is one of the fluorophosphoric acids. It is produced when phosphoryl fluoride reacts with water. POF3 + H2O → HPO2F2 + HF. This in turn is hydrolysed more to give monofluorophosphoric acid, and a trace of hexafluorophosphoric acid. HPO2F2 also is produced when HF reacts with phosphorus pentoxide. Yet another method involves making difluorphosphoric acid as a side product of calcium fluoride being heated with damp phosphorus pentoxide. A method to make pure difluorphosphoric acid involves heating phosphoryl fluoride with monofluorophosphoric acid and separating the product by distillation. POF3 + H2PO3F → 2HPO2F2.
Difluorophosphoric acid can also be produced by fluorinating phosphorus oxychlorides. P2O3Cl4 and POCl3 react with hydrogen fluoride solution to yield HPO2Cl2 and then HPO2F2. Yet another way is to treat orthophosphate with fluorosulfuric acid.
Difluorphosphoric acid melts at −96.5 °C and boils at 115.9 °C. Its density at 25 °C is 1.583.

Phosphoryl difluoride oxide

Difluorophosphoric acid anhydride also known as phosphoryl difluoride oxide or diphosphoryl tetrafluoride is an anhydride of difluorphosphoric acid. It crystallises in the orthorhombic system, with space group Pcca and Z = 4. P2O3F4 can be made by refluxing difluorophosphoric acid with phosphorus pentoxide. P2O3F4 boils at 71 °C.

Substitution

In addition to the isoelectronic series, ions related by substituting fluorine or oxygen by other elements include monofluorophosphate, difluorothiophosphate, dichlorothiophosphate, dichlorophosphate, chlorofluorothiophosphate, chlorofluorophosphate, dibromophosphate, and bromofluorophosphate.

Adducts

Difluorophosphate can form adducts with PF5 and AsF5. In these the oxygen atoms form a donor-acceptor link between the P and As atoms, linking the difluorides to the pentafluorides. Example salts include KPO2F2·2AsF5, KPO2F2·AsF5, KPO2F2·2PF5 and KPO2F2·PF5.
Amines can react with phosphoryl fluoride to make substances with a formula RR′N–POF2. The amines shown to do this include ethylamine, isopropylamine, n-butylamine, tert-butylamine, dimethylamine, and diethylamine. The monoamines can further react to yield an alkyliminophosphoricfluoride.