Phosphinates or hypophosphites are a class of phosphorus compounds conceptually based on the structure of hypophosphorous acid. IUPAC prefers the term phosphinate in all cases, however in practice hypophosphite is usually used to describe inorganic species (e.g. sodium hypophosphite), while phosphinate typically refers to organophosphorus species.

Hypophosphites

The hypophosphite ion is . The salts are prepared by heating white phosphorus in warm aqueous alkali e.g. Ca(OH)2:

P4 + 2 Ca(OH)2 + 4 H2O → 2 Ca(H2PO2)2 + 2 H2

Hypophosphites are reducing agents:

+ 3 OH− → + 2 H2O + 2 e−

Hypophosphites are used in electroless nickel plating as the reducing agent to deposit for example Ni metal from Ni salts. The hypophosphite ion is thermodynamically unstable, and disproportionates on heating to phosphine and phosphate salts:

2 → PH3 +

Reactions When heated, sodium hypophosphite disproportionates to PH3, Na2H2P2O5, Na2HPO3, Na4P2O7 and H2.

When exposed to light ammonium hypophosphite darkens. A proposed reaction is:

[H2PO2]− → H• + [HP•O2]− [HP•O2]− + [H2PO2]− → H• + [O2P•PHO2]2−

Uses Hypophosphite (usually sodium hypophosphite) acts as a reducing agent to deposit nickel onto surfaces without using electricity. Common in electronics, automotive, and aerospace industries for corrosion resistance and hardness. Some hypophosphite compounds are used in medicines, particularly as sources of phosphorus or as stabilizers in formulations.

In polymer and plastic stabilization, they are used today as antioxidants and thermal stabilizers to prevent degradation during the processing of plastics like PVC. Beyond nickel plating, hypophosphites are used in general chemical synthesis where a mild reducing agent is needed.

Additionally, in wood science, sodium hypophosphite in combination with other agents, such as ammonium-, nitrogen- or aluminium-containing chemicals, has been used for in solid wood and particleboard to improve the fire retarding properties. List nameformulasystemspace groupunit cellvolumedensitycommentreflithium dihydrogenphosphateLiH2PO2monoclinicC2/ca = 9.356 b = 5.3107 c = 6.543 β = 108.26° Z=4308.731.547beryllium bis(dihydrogenphosphate)Be(H2PO2)2tetragonalP41212a = 5.0117 c = 20.051 Z=4503.621.833band gap 7.84 eVammonium hypophosphite(NH4)H2PO2orthorhombicCmmaa = 7.5425 b = 11.5204 c = 3.9942 Z = 4347.071.589Hydrazinium(2+) phosphinate(N2H6)(H2PO2)2monoclinicP21/ca = 7.74 b = 6.44 c = 6.77 β = 98.1°1,3-diaminoguanidinium(1+) hypophosphite(CN5H8)H2PO2monoclinicP21/c ?P21/ma=6.3673 b=14.5302 c=66452 β=16742°triethylammonium hypophosphite hydrate(Et3NH)(H2PO2)·H2ONaH2PO2•0.8H2OmonoclinicP21/na=11.127 b=13.572 c=12.93 β=102.98° Z=20Mg(H2PO2)2Mg(PO2H2)2.6H2OtetragonalI41/acda=10.33 c=20.38 Z=81.60hexaaquamagnesium(II) bis(hypophosphite)[Mg(H2O)6](H2PO2)2tetragonalP42/nmca=7.2187 c=10.4639 Z=2542.271.598Al(H2PO2)3Potassium hypophosphiteKH2PO2monoclinicC2/ca = 7.313 b = 7.2952 c = 7.181 β = 116.20° Z = 4343.75calcium hypophosphiteCa(H2PO2)2calcium sodium hypophosphiteNaCa(H2PO2)2cubicP213a = 9.720918.31.90Ti(H2PO2)3trigonalR3ca=11.7484 c=9.7368 Z=61163.92.079bluevanadium(III) hypophosphiteV(H2PO2)3monoclinicP21/na = 11.4985 b = 11.7771 c = 11.5999 β = 99.807°1547.892.11greenVO(H2PO2)·H2OmonoclinicC2/ca = 12.046 b = 8.147 c = 7.548 β = 121.83°bluemanganese hypophosphite monohydrateMn(H2PO2)2.H2OmonoclinicP21/ca = 7.8601 b = 7.4411 c = 10.7717 β = 102.859° Z=4manganese hypophosphite monohydrateβ-Mn(H2PO2)2.H2OmonoclinicP21/n12.013 b=8.100 c=12.450 β=106.28° Z=8(μ3-Hypophosphito)-(μ2-hypophosphito)-manganese dimethylformamide solvate[Mn(H2PO2)2]n·(DMF)0.11hexagonalRa=20.53 c=8.041[NH4][MnII(H2PO2)3(H2O)]monoclinicP21/na=7.4412 b=15.147 c=9.3051 β=108.230°guanidinium manganese hypophosphiteCN3H6 Mn(H2POO)3monoclinicI2/ma=8.7596 b=13.2087 c=9.6956 β=89.764°guanidinium manganese hypophosphiteCN3H6 Mn(H2POO)3triclinicPa=9.0994 b=9.2419 c=15.8369 α=105.294° β=90.971° γ=118.618°formamidinium manganese hypophosphiteCN2H5Mn(H2POO)3monoclinicC2/ca=13.4506 b=10.2196 c=7.5274 β=103.604°imidazolium manganese hypophosphiteC3H52Mn(H2POO)3monoclinicP21/ca=9.6520 b=12.7066 c=18.4643 β=91.5450°triazolium manganese hypophosphiteC2H4N3Mn(H2POO)3monoclinicP21/ca=9.8034 b=8.5924 c=13.3120 β=98.554°dabcon-diium dimanganese hexakis(hypophosphite)C6H14N2Mn2(H2POO)6hexagonalRa=9.8860 c=41.171dabcon-diium dimanganese hexakis(hypophosphite)C6H14N2Mn2(H2POO)6triclinicPa=9.8364( b=14.9329 c=16.8019 α=66.631° β=89.585° γ=89.082°bis(μ2-Phosphinato)-bis(5,10,15,20-tetraphenylporphyrinato)-di-manganese ethanol solvate monohydratemonoclinicP21/na=13.2131 b=25.263 c=23.477 β=95.31°Bis(phosphinato)(2,2'-bipyridyl)manganese(II)C10H12N2Mn(H2PO2)2monoclinicC2/ca=16.827 b=10.745 c=7.170 β=91.46° X=41.75yellowiron(III) hypophosphiteFe(H2PO2)3hexagonalRa = 11.2800 c = 9.6375 Z = 61061.972.353hexaaquacobalt(II) bis(hypophosphite)[Co(H2O)6](H2PO2)2tetragonalI41/acda=10.3406 c=20.402 Z=82181.61.809purpleCo(H2PO2)2•0.53H2OmonoclinicP112/aa=6.4722 b=5.3411 c=7.4900 γ=90.087° Z=2layered, can intercallate with more water, or pyridineCo(H2PO2)2•2H2O[NH4][CoII(H2PO2)3(H2O)]monoclinicP21/na=7.367 b=14.914 c=9.205 β=108.38°CoCl(H2PO2).H2OorthorhombicPbcaa=7.416 b=13.082 c=9.483 Z=89202.56bis(μ-hypophosphito)-bis(benzene-1,2-diamine)-cobalt dichloride[Co(H2PO2)(C12N4H16)]Cl2orthorhombicPbcna = 9.554 b = 9.147 c = 21.9222 Z = 21915.7ortho-phenylenediamine cobalt hypophosphite chloride[Co(H2PO2)(C12N4H16)]Cl2orthorhombicPbcna = 9.554 b = 9.147 c = 21.9222 Z = 21915.7CoIII(NH3)5(H2PO2)(ClO4)2NaCo(H2PO2)3cubicP213a = 9.256 Z=4793.1Hexaaquanickel(II) bis(hypophosphite)[Ni(H2O)6](H2PO2)2monoclinicC2/ca = 10.1453 b = 10.1467 c = 10.3571 β = 92.632 Z=41065.051.851green[NH4][NiII(H2PO2)3(H2O)]monoclinicP21/na=7.3202 b=14.7961 c=9.1762 β=108.814°(μ2-13,27-Di-t-butyl-3,6,9,17,20,23-hexamethyl-3,6,9,17,20,23-hexaazatricyclo[23.3.1.111,15]triaconta-1(29),11(30),12,14,25,27- hexaene-29,30-dithiolato)-(μ2-phosphinato-O,O')-di-nickel(ii) tetraphenylborate acetonitrile solvate[Ni2L(μ-O2PH2)]BPh4triclinicPa=13.179 b=15.736 c=16.799 α=108.48° β=91.90° γ=107.61°"[Ni2L(μ-O2PH2)]ClO4NiCl(H2PO2).H2OorthorhombicPbcaa = 7.2986 b = 13.0616 c = 9.4078 Z = 4896.85pale green; hypophosphitehexaaquacobalt(II)/nickel(II) bis(hypophosphite)[Co0.5Ni0.5(H2O)6](H2PO2)2tetragonalI41/acd a=10.3111 c=20.236 Z=82163.21.823greenCu(H2PO2)2monoclinicP21/ca = 7.2186 b = 5.3462 c = 6.2521 β = 98.835° Z = 2 T = 270 238.422.696blueCu(H2PO2)2orthorhombicPbcaa = 5.3259 b = 6.2720 c = 14.2590 Z=4 T = 270 476.312.699blueCu(H2PO2)2orthorhombicPnmaa = 6.6738 b = 5.4133 c = 7.1954 Z=2 T = 270 259.952.472blueZn(H2PO2)2orthorhombicPmmaa=6.479 b=5.365 c=7.408Zn(H2PO2)2.H2OmonoclinicP21/ca=7.685 b=7.376 c=10.468 β=104.16°Ge2(H2PO2)6trigonalRa=11.86 c=9.58 Z=32.18colourlessChloro(phosphinato)germanium(II)GeCl(H2PO2)orthorhombicPnama=8.178 b=9.595 c=5.299 Z=42.764Rubidium hypophosphiteRbH2PO2orthorhombicPnmaa = 7.9835 b = 6.3678 c = 7.575 Z = 4385.12Sr(H2PO2)2monoclinicC2/ca = 15.655 b = 5.9436 c = 5.9177 β = 93.905° Z=4549.42.631colourlessCadmium bis[dihydrogenphosphate(I)]Cd(H2PO2)2•H2OmonoclinicC2/ca = 15.156 b = 5.4692 c = 6.5516 β=102.487 Z=4530.223.036Chloro(phosphinato)tin(II)SnCl(H2PO2)orthorhombicPnama=8.045 b=9.915 c=5.517 Z=43.308Calcium hexakis(dihydrogenphosphito)stannate(IV)Ca[Sn(H2PO2)6]hexagonalRa = 11.8619 c = 9.8668 Z = 31202.312.273[Sn2(H2PO2)3]BrorthorhombicPmn21a=5.4177 b=7.1467 c=13.8359 Z=2535.713.176 RbSb(SO4)(H2PO2)ForthorhombicPnmaa=15.1004 b=5.4481 c=8.8857 Z=4731.013.519darkCesium hypophosphiteCsH2PO2orthorhombicPnmaa = 8.3776 b = 6.6271 c = 7.916 Z = 4439.52barium bis(dihydrogenphosphate)Ba(H2PO2)2orthorhombicCccaa = 6.2390 b = 15.584 c = 6.1726 Z=4600.22.958colourlessBaSb(H2PO2)3Cl2monoclinicP21a=8.5451 b=7.6108 c=9.0163 β=95.680°SHG 5.0 × KDP; birefringence (0.09@546 nm); bandgap 4.2 eVLa(H2PO2)3triclinicPa = 6.7912 b = 7.0801 c = 8.863 α = 82.64° β = 74.43o γ = 71.91° Z=2La(H2PO2)3•H2OtriclinicPa = 7.2291 b = 7.983 c = 8.934 α =110.57° β = 98.26° γ = 104.35° Z=2Ce(H2PO2)3(H2O)triclinicPa=7.1729 b=7.9827 c=8.871 α=110.643° β=98.101° γ=104.97°Pr(H2PO2)3[Pr(H2PO2)(HPO3)(H2O)]·H2OorthorhombicP212121a=6.6558 b=7.1539 c=16.5506Nd(H2PO2)3Dy(H2PO2)3monoclinicC2/ma=14.368 b=5.734 c=12.123 β=122.33°Yb(H2PO2)3monoclinicC2/ma=14.281 b =5.658 c=12.006 β=122.26°Thallous hypophosphiteTlH2PO2melt 114°CPb(H2PO2)2monoclinicC2/ca = 15.516 b = 6.008 c = 5.969 β = 93.30° Z=4555.54.032colourlessU(H2PO2)4orthorhombicPbcaa=7.467 b=13.394 c=19.904 Z=81990.73.323greenUO2(H2PO2)2·H2OmonoclinicP21/na = 7.686 b = 9.275 c = 11.027 β = 92.32° Z=4785.43.535colourlessUO2(H2PO2)2·H3POorthorhombicP212121a = 7.1572 b = 7.2363 c = 17.554901.03.435yellow

See also Organophosphinic acid Phosphine - PR3 Phosphine oxide - OPR3 Phosphite - P(OR)3 Phosphonate - OP(OR)2R Phosphate - OP(OR)3

References