Difluorophosphate Explained

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.[1] 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.[2] This was how the ion was first made by its discoverer, Willy Lange, in 1929.[3] [4]

Alkali metal chlorides can react with dry difluorophosphoric acid to form alkali metal salts.[5]

Fluorination of dichlorophosphates can produce difluorophosphates.[6] Another method is fluorination of phosphates or polyphosphates.[4]

Trimethylsilyl difluorophosphate reacts with metal chlorides to give difluorophosphates.[7]

The anhydride of difluorophosphoric acid, phosphoryl difluoride oxide reacts with oxides such as to yield difuorophosphates.[8] Phosphoryl difluoride oxide also reacts with alkali metal fluorides to yield difluorophosphates.[9]

Properties

The difluorophosphate ion in ammonium difluorophosphate and potassium difluorophosphate has these interatomic dimensions:[10]

Difluorophosphate salt P–O length P–F length O–P–O angle F–P–O angle F–P–F angle
Ammonium difluorophosphate1.457 Å1.541 Å118.7°109.4°98.6°
Potassium difluorophosphate1.470 Å1.575 Å122.4°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.[11] [12]

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 .[13] [14]

Compounds

FormulaNameStructureInfrared spectrumMelting pointCommentsReference
Lithium difluorophosphate360 °C
Beryllium difluorophosphate>400 °C prepared from and acid[15]
Ethyl difluorophosphate
Ammonium difluorophosphateorthorhombic: a = 8.13 Å, b = 6.43 Å, c = 7·86 Å, Z = 4 space group PnmaP–F stretching 842 and 860 cm−1; P–O stretching 1138 and 1292 cm−1213 °C
Nitronium difluorophosphate515, 530, 550, 560, 575, 845, 880, 1145, 1300, 2390, 3760 cm−1nitronium formed from anhydride and [16]
Nitrosonium difluorophosphate500, 840, 880, 1130, 1272, 1315, 2278 cm−1nitrosonium formed from anhydride and
Sodium difluorophosphate210 °C
Magnesium difluorophosphate200 °C
Ammonium magnesium difluorophosphateCmcm a=5.411 b=15.20 c=12.68[17]
Aluminium difluorophosphatepolymeric505, 541, 582, 642, 918, 971, 1200, 1290 cm−1 (with 355 cm−1 impurity)formed from and acid; colourless insoluble powder
Silicon(IV) difluorophosphateformed from and anhydride[18]
Trimethylsilyl difluorophosphateformed from anhydride and
Potassium difluorophosphateorthorhombic: a = 8.03 Å, b = 6.205 Å, c = 7.633 Å, Z = 4, V=380.9 Å3, density = 2.44 g/cm3510, 525, 570, 835, 880, 1145, 1320, 1340 cm−1263 °Ccolourless elongated prisms[19] [20]
Tetrapotassium difluorophosphate pyrosulfateC2/c: a = 13.00 Å, b = 7.543 Å, c = 19.01 Å, β = 130.07°, Z = 4[21]
Calcium difluorophosphate - ethyl acetate 1:1 solvate[22]
Calcium difluorophosphate>345 °C
Pervanadyl difluorophosphate
Chromyl difluorophosphateformed from anhydride; red-brown[23]
Chromium(III) difluorophosphate320, 385, 490, 575, 905, 955, 1165, 1255 cm−1formed from excess anhydride, green
184 °C[24]
dissolve manganese in acid; white
[25]
Iron(II) difluorophosphate463, 496, 668 (weak), 869 (double), 1139, 1290 cm−1180 °C colour blue green, hygroscopic, melts 250 °C, above 300 °C starts decomposing to
Iron(III) difluorophosphate262, 493, 528, 570, 914, 965, 1173, 1242 cm−1>400 °Cdecomposes at 230 °C yielding ; dissolve iron in acid in presence of oxygen
Cobalt(II) difluorophosphate173 °Cprepared from and acid; pink or blue; blue formed by heating pink to 140 °C
dissolve cobalt in acid; red-purple[26]
Cobalt(II) difluorophosphate - methyl cyanide solvate 1:2orthorhombic: a = 9.227 Å, b = 13.871 Å, c = 9.471 Å, V = 1212 Å3, Z = 4, density = 1.88 g/cm3treat with for a few weeks; red crystals
Nickel(II) difluorophosphate255 °C slowly prepared from and acid; yellow
dissolve nickel in acid; yellow
Copper(II) difluorophosphateorthorhombic Fddd: a = 10.134 Å, b = 24.49 Å, c = 34.06 Å, Z = 48, V = 8454.3 Å3, density = 2.50 g/cm3265 °C pale blue needles[27]
polymeric; monoclinic: a = 12.435 Å, b = 10.887 Å, c = 25.682 Å, β = 100.220°, V = 3421 Å3colourless[28]
Zinc(II) difluorophosphate °C?glassy
Tetra(difluorophosphato)zincic(II) acid
Gallium(III) difluorophosphate
Dimethylgallium(III) difluorophosphatedimeric380, 492, 520, 551, 616, 709, 750, 899, 949, 1171, 1218, 1262, 1295, 1404, 2922, 2982 cm−1[29]
Rubidium difluorophosphateorthorhombic: a = 8.15 Å, b = 6.45 Å, c = 7.79 Å, Z = 4, V = 409.5 Å3 density = 3.02 g/cm3P–F stretching 827 and 946 cm−1; P–O stretching 1145 and 1320 cm−1160 °Cwhite
Strontium difluorophosphate250 °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[30]
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[31]
Ag(4,4′-dicyanodiphenylacetylene)
Cadmium(II) difluorophosphate245 °C
Indium(III) difluorophosphate269, 492, 528, 567, 910, 962, 1179, 1269 cm−1white, decomposes at 260 °C yielding
Dimethylindium(III) difluorophosphatedimeric373, 490, 500, 535, 559, 735, 878, 925, 1128, 1179, 1275, 1435, 2928, 3000 cm−1
Tin(IV) dichloride difluorophosphate[32]
Dimethyltin(IV) difluorophosphate204 °C prepared from and acid; yellow
Diethyltin(IV) difluorophosphate262 °C prepared from and acid; yellow
Dipropyltin(IV) difluorophosphate245 °C prepared from and acid; yellow
Dibutyltin(IV) difluorophosphate235 °C prepared from and acid; yellow
Dioctyltin(IV) difluorophosphate114 °Cprepared from and acid; yellow
Antimony(V) tetrachloride difluorophosphate
Antimony(V) tetrafluoride difluorophosphate
(2,2-dipyradyl)
Au[bis(triphenylphosphine sulfide-''S'')][33]
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[34]
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[35]
Xenon(II) difluorophosphate
Caesium difluorophosphateorthorhombic: a = 8.437 Å, b = 6.796 Å, c = 8.06 Å, Z = 4, V = 462.1 Å3, density = 3.36 g/cm3286 °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°
[36]
Mercury(II) difluorophosphate
Mercury(I) difluorophosphate or di(difluorophosphato)dimercuraneRaman

220 cm−1

produced from anhydride
Thallium(I) difluorophosphateproduced from anhydride, or acid on TlCl
Dimethylthallium(III) difluorophosphatedimeric360, 374, 500, 505, 520, 559, 850, 880, 1120, 1140, 1195, 1250, 1285, 2932, 3020 cm−1
Lead(II) difluorophosphate189 °C
Uranyl difluorophosphate260, 498, 854, 924, 980, 1124 cm−1IR spectrum due to
Tetraethylammonium difluorophosphate[37]
1-ethyl-3-methylimidazolium difluorophosphateionic liquid[38]
1-butyl-3-methylimidazolium difluorophosphateionic liquid
1-butyl-1-methylpyrrolidinium difluorophosphateionic liquid
1-butyl-1-methylpiperidinium difluorophosphateionic liquid
di(3,3′,4,4′-tetramethyl-2,2′,5,5′-tetraselenafulvalenium)difluorophosphateTransitions to a metallic state below [39]
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 = 4insoluble; yellow-brown
Strychnine
Cocaine
Brucine
Morphine
Tetramethylammonium difluorophosphate
Tetra(difluorophosphato)boric acid469, 502, 552, 647, 836, 940, 994, 1093, 1348, 1567 cm−1formed from and acid; liquid
Lithium tetra(difluorophosphato)boratemonoclinic 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 and butyllithium; colourless
Dimethylsulfonium tetra(difluorophosphato)borate472, 511, 555, 648, 832, 933, 993, 1082, 1337, 1436, 2851, 2921, 3042 cm−1formed from and acid; ionic liquid
(Diethyl ether)lithium hexa(difluorophosphato)aluminatetrigonal 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 butyllithium and triethylaluminium and the acid; white
305, 370, 485, 550, 870, 920, 1050, 1130, 1250 cm−1145 °C formed from anhydride and ; brown
amorphous280, 490, 620, 880, 915, 950, 1020, 1070, 1140, 1280 cm−1125 °C formed from anhydride and ; white
amorphous280, 474, 620, 930, 1030, 1130, 1230 cm−1109 °C formed from anhydride and ; white

Related substances

Difluorphosphoric 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 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:[40]

Difluorophosphoric acid can also be produced by fluorinating phosphorus oxychlorides. and react with hydrogen fluoride solution to yield and then .[41] Yet another way is to treat orthophosphate with fluorosulfuric acid .[42]

Difluorphosphoric acid is a colorless liquid. It melts at and boils at . Its density at 25 °C is 1.583 g/cm3.[43]

Phosphoryl difluoride oxide

Difluorophosphoric acid anhydride also known as phosphoryl difluoride oxide or diphosphoryl tetrafluoride (or) is an anhydride of difluorphosphoric acid. It crystallises in the orthorhombic system, with space group Pcca and Z = 4.[44] can be made by refluxing difluorophosphoric acid with phosphorus pentoxide. boils at 71 °C.[45]

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.[46]

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 .[47]

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 alkyliminophosphoric fluoride .[48]

Notes and References

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