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 Ammonium 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 metal chlorides can react with dry difluorophosphoric acid to form alkali metal salts.
Fluorination of dichlorophosphates can produce difluorophosphates. Another method is fluorination of phosphates or polyphosphates.
Trimethylsilyl difluorophosphate () reacts with metal chlorides to give difluorophosphates.
The anhydride of difluorophosphoric acid (), phosphoryl difluoride oxide () reacts with oxides such as to yield difluorophosphates. Phosphoryl difluoride oxide also reacts with alkali metal fluorides to yield difluorophosphates.
Properties The difluorophosphate ion in ammonium difluorophosphate and potassium difluorophosphate has these interatomic dimensions:
Difluorophosphate salt P–O length P–F length O–P–O angle F–P–O angle F–P–F angle Ammonium difluorophosphate 1.457 Å 1.541 Å 118.7° 109.4° 98.6° Potassium difluorophosphate 1.470 Å 1.575 Å 122.4° 108.6° 97.1°
Hydrogen bonding from ammonium ion to oxygen atoms causes a change to the difluorophosphate ion in the ammonium salt.
On heating the salts that are not of alkali metals or alkaline earth metals, difluorophosphates decompose firstly by giving off 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 , and .
Compounds
FormulaNameStructureInfrared spectrumMelting pointCommentsReference Lithium difluorophosphate 360 °C Beryllium difluorophosphate>400 °C prepared from and acid Ethyl difluorophosphate Ammonium difluorophosphate orthorhombic: a = 8.13 Å, b = 6.43 Å, c = 7·86 Å, Z = 4 space group Pnma P–F stretching 842 and 860 cm−1; P–O stretching 1138 and 1292 cm−1 213 °C Nitronium difluorophosphate 515, 530, 550, 560, 575, 845, 880, 1145, 1300, 2390, 3760 cm−1 nitronium formed from anhydride and Nitrosonium difluorophosphate 500, 840, 880, 1130, 1272, 1315, 2278 cm−1 nitrosonium formed from anhydride and Sodium difluorophosphate 210 °C Magnesium difluorophosphate 200 °C Ammonium magnesium difluorophosphateCmcm a=5.411 b=15.20 c=12.68 Aluminium difluorophosphate polymeric 505, 541, 582, 642, 918, 971, 1200, 1290 cm−1 (with 355 cm−1 impurity) formed from and acid; colourless insoluble powder Silicon(IV) difluorophosphate formed from and anhydride Trimethylsilyl difluorophosphate formed from anhydride and Potassium difluorophosphate orthorhombic: a = 8.03 Å, b = 6.205 Å, c = 7.633 Å, Z = 4, V=380.9 Å3, density = 2.44 g/cm3 510, 525, 570, 835, 880, 1145, 1320, 1340 cm−1 263 °C colourless elongated prisms Tetrapotassium difluorophosphate pyrosulfateC2/c: a = 13.00 Å, b = 7.543 Å, c = 19.01 Å, β = 130.07°, Z = 4 Calcium difluorophosphate - ethyl acetate 1:1 solvate Calcium difluorophosphate>345 °C Pervanadyl difluorophosphate Chromyl difluorophosphate formed from anhydride; red-brown Chromium(III) difluorophosphate 320, 385, 490, 575, 905, 955, 1165, 1255 cm−1 formed from excess anhydride, green 184 °C dissolve manganese in acid; white Iron(II) difluorophosphate 463, 496, 668 (weak), 869 (double), 1139, 1290 cm−1 180 °C colour blue green, hygroscopic, melts 250 °C, above 300 °C starts decomposing to Iron(III) difluorophosphate 262, 493, 528, 570, 914, 965, 1173, 1242 cm−1>400 °C decomposes at 230 °C yielding ; dissolve iron in acid in presence of oxygen Cobalt(II) difluorophosphate 173 °C prepared from and acid; pink or blue; blue formed by heating pink to 140 °C dissolve cobalt in acid; red-purple Cobalt(II) difluorophosphate - methyl cyanide solvate 1:2 orthorhombic: a = 9.227 Å, b = 13.871 Å, c = 9.471 Å, V = 1212 Å3, Z = 4, density = 1.88 g/cm3 treat with for a few weeks; red crystals Nickel(II) difluorophosphate 255 °C slowly prepared from and acid; yellow dissolve nickel in acid; yellow Copper(II) difluorophosphate orthorhombic Fddd: a = 10.134 Å, b = 24.49 Å, c = 34.06 Å, Z = 48, V = 8454.3 Å3, density = 2.50 g/cm3 265 °C pale blue needles polymeric; monoclinic: a = 12.435 Å, b = 10.887 Å, c = 25.682 Å, β = 100.220°, V = 3421 Å3 colourless Zinc(II) difluorophosphate °C? glassy Tetra(difluorophosphato)zincic(II) acid Gallium(III) difluorophosphate Dimethylgallium(III) difluorophosphate dimeric 380, 492, 520, 551, 616, 709, 750, 899, 949, 1171, 1218, 1262, 1295, 1404, 2922, 2982 cm−1 Rubidium difluorophosphate orthorhombic: a = 8.15 Å, b = 6.45 Å, c = 7.79 Å, Z = 4, V = 409.5 Å3 density = 3.02 g/cm3 P–F stretching 827 and 946 cm−1; P–O stretching 1145 and 1320 cm−1 160 °C white Strontium difluorophosphate 250 °C prepared from and acid Ammonium strontium difluorophosphateTriclinic P a=7.370 b=11.054 c=13.645 α=88.861 β=87.435° γ=89.323° Silver(I) difluorophosphate Ag(1-methyl-2-alkylthiomethyl-1H-benzimidazole) Ag(2,6-bis-[(2-methylthiophenyl)-2-azaethenyl]pyridine) Triclinic P1: a = 7.687 Å, b = 10.740 Å, c = 13.568 Å, α = 99.52°, β = 96.83°, γ = 99.83°, Z = 2, V = 1076 Å3, density = 1.81 g/cm3 Ag(4,4′-dicyanodiphenylacetylene) Cadmium(II) difluorophosphate 245 °C Indium(III) difluorophosphate 269, 492, 528, 567, 910, 962, 1179, 1269 cm−1 white, decomposes at 260 °C yielding Dimethylindium(III) difluorophosphate dimeric 373, 490, 500, 535, 559, 735, 878, 925, 1128, 1179, 1275, 1435, 2928, 3000 cm−1 Tin(IV) dichloride difluorophosphate Dimethyltin(IV) difluorophosphate 204 °C prepared from and acid; yellow Diethyltin(IV) difluorophosphate 262 °C prepared from and acid; yellow Dipropyltin(IV) difluorophosphate 245 °C prepared from and acid; yellow Dibutyltin(IV) difluorophosphate 235 °C prepared from and acid; yellow Dioctyltin(IV) difluorophosphate 114 °C prepared from and acid; yellow Antimony(V) tetrachloride difluorophosphate Antimony(V) tetrafluoride difluorophosphate (2,2-dipyradyl) Au[bis(triphenylphosphine sulfide-S)] Raman: 130, 163, 191, 219, 295, 323, 329, 378, 637, 713, 737, 781, 799, 839, 918, 1163 cm−1 yellowish colour, produced from , decomposed by water Raman: 217, 247, 269, 305, 343, 367, 395, 473, 569, 643, 671, 717, 797, 891, 1123 cm−1 yellowish colour, produced from , decomposed by water Xenon(II) fluoride difluorophosphate Xenon(II) difluorophosphate Caesium difluorophosphate orthorhombic: a = 8.437 Å, b = 6.796 Å, c = 8.06 Å, Z = 4, V = 462.1 Å3, density = 3.36 g/cm3 286 °C Barium difluorophosphateorthorhombic I2d a =10.4935 b =10.4935 c =26.030>400 °C Diammonium barium difluorophosphateP2/n a=14.285 b=5.472 c=19.474 β=97.607°KBaSr(PO2F2)(PO3F)2P21/c a=7.0638 b=7.4306 =21.3633 β=93.386°, V=1119.37 Å3 Z=4birefringence 0.042@550 nm Mercury(II) difluorophosphate Mercury(I) difluorophosphate or di(difluorophosphato)dimercurane Raman: 220 cm−1 produced from anhydride Thallium(I) difluorophosphate produced from anhydride, or acid on TlCl Dimethylthallium(III) difluorophosphate dimeric 360, 374, 500, 505, 520, 559, 850, 880, 1120, 1140, 1195, 1250, 1285, 2932, 3020 cm−1 Lead(II) difluorophosphate 189 °C Uranyl difluorophosphate 260, 498, 854, 924, 980, 1124 cm−1 IR spectrum due to Tetraethylammonium difluorophosphate 1-ethyl-3-methylimidazolium difluorophosphate ionic liquid 1-butyl-3-methylimidazolium difluorophosphate ionic liquid 1-butyl-1-methylpyrrolidinium difluorophosphate ionic liquid 1-butyl-1-methylpiperidinium difluorophosphate ionic liquid di(3,3′,4,4′-tetramethyl-2,2′,5,5′-tetraselenafulvalenium)difluorophosphate Transitions to a metallic state below 1,4-diphenyl-3,5-enanilo-4,5-dihydro-1,2,4-triazole (nitron)monoclinic P21/n: a = 7.3811 Å, b = 14.9963 Å, c = 16.922 Å, β = 102.138°, V = 1361.2 Å3, Z = 4 insoluble; yellow-brown Strychnine Cocaine Brucine Morphine Tetramethylammonium difluorophosphate Tetra(difluorophosphato)boric acid 469, 502, 552, 647, 836, 940, 994, 1093, 1348, 1567 cm−1 formed from and acid; liquid Lithium tetra(difluorophosphato)borate monoclinic P21/c: a=7.9074 Å, b = 14.00602 Å, c = 13.7851 Å, β = 121.913°, Z = 4 479, 502, 568, 833, 945, 1002, 1080, 1334 cm−1 formed from and butyllithium; colourless Dimethylsulfonium tetra(difluorophosphato)borate 472, 511, 555, 648, 832, 933, 993, 1082, 1337, 1436, 2851, 2921, 3042 cm−1 formed from and acid; ionic liquid (Diethyl ether)lithium hexa(difluorophosphato)aluminate trigonal R: a = 17.4058 Å, b = 17.4058 Å, c = 21.4947 Å, γ = 120°, Z = 6 417, 503, 536, 624, 723, 891, 922, 964, 1174, 1204, 1283 cm−1 formed from butyllithium and triethylaluminium and the acid; white 305, 370, 485, 550, 870, 920, 1050, 1130, 1250 cm−1 145 °C formed from anhydride and ; brown amorphous 280, 490, 620, 880, 915, 950, 1020, 1070, 1140, 1280 cm−1 125 °C formed from anhydride and ; white amorphous 280, 474, 620, 930, 1030, 1130, 1230 cm−1 109 °C formed from anhydride and ; white
Related substances
Difluorophosphoric acid Difluorophosphoric acid () is one of the fluorophosphoric acids. It is produced when phosphoryl fluoride reacts with water:
This in turn is hydrolysed more to give monofluorophosphoric acid (), and a trace of hexafluorophosphoric acid (). also is produced when HF reacts with phosphorus pentoxide. Yet another method involves making difluorophosphoric acid as a side product of calcium fluoride being heated with damp phosphorus pentoxide. A method to make pure difluorophosphoric acid involves heating phosphoryl fluoride with monofluorophosphoric acid and separating the product by distillation:
Difluorophosphoric acid can also be produced by fluorinating phosphorus oxychlorides. and react with hydrogen fluoride solution to yield and then . Yet another way is to treat orthophosphate () with fluorosulfuric acid ().
Difluorophosphoric acid is a colorless liquid. It melts at and boils at . Its density at 25 °C is 1.583 g/cm3.
Phosphoryl difluoride oxide Difluorophosphoric acid anhydride also known as phosphoryl difluoride oxide or diphosphoryl tetrafluoride ( or ) is an anhydride of difluorophosphoric acid. It crystallises in the orthorhombic system, with space group Pcca and Z = 4. Originally in Inorg. Chem. 49 (2010) 6, 3002–3010 can be made by refluxing difluorophosphoric acid with phosphorus pentoxide. 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, , , , and .
Adducts Difluorophosphate can form adducts with and . In these the oxygen atoms form a donor-acceptor link between the P and As (or P) atoms, linking the difluorides to the pentafluorides. Example salts include , , and . Full article at Eur. J. Solid State Inorg. Chem. 33 (1996) 9, 865–877
Amines can react with phosphoryl fluoride to make substances with a formula . The amines shown to do this include ethylamine, isopropylamine, n-butylamine, t-butylamine, dimethylamine, and diethylamine. The monoamines can further react to yield an ().
References