The Nickel oxyacid salts are a class of chemical compounds of nickel with an oxyacid. The compounds include a number of minerals and industrially important nickel compounds.

Nickel(II) sulfate can crystallise with six water molecules yielding Retgersite or with seven making Morenosite which is isomorphic to Epsom salts. These contain the hexaquanickel(II) ion. There is also an anhydrous form, a dihydrate and a tetrahydrate, the last two crystallised from sulfuric acid. The hexahydrate has two forms, a blue tetragonal form, and a green monoclinic form, with a transition temperature around 53 °C.Mellor pp462-465 The heptahydrate crystallises from water below 31.5 °C above this blue hexahydrate forms, and above 53.3 °C the green form.Mellor p 466-467 Heating nickel sulfate dehydrates it, and then 700 °C it loses sulfur trioxide, sulfur dioxide and oxygen.

Nickel sulfite can be formed by bubbling sulfur dioxide through nickel carbonate suspended in water. A solution is formed that slowly loses sulfur dioxide, and which crystallises nickel sulfite hexahydrate. Crystals are frequently in the shape of stars, caused by the two opposite triangular enantiomorphs growing base to base. Nickel sulfite hexahydrate is highly piezoelectric. Optically it is uniaxial negative with refractive indexes ω=1.552 ε=1.509. When heated it dehydrates and then decomposes producing nickel oxide and nickel sulfate.

Nickel thiosulfate (NiS2O3) has the same structure as the magnesium salt. It has alternating layers of octahedral shaped nickel(II) hexahydrate, and tetrahedral shaped S2O32− perpendicular to the β direction. When heated to 90 °C it decomposes to form NiS. NiS2O3 can be made from BaS2O3 and NiSO4.

Nickel sulfamate can be used for nickel or mixed nickel-tungsten plating. It can be formed by the action of sulfamic acid on nickel carbonate.

Nickel selenite (NiSeO3) has many different hydrates, anhydrous NiSeO3, NiSeO3, NiSeO3 (which is also a mineral called ahlfeldite), and NiSeO3.

Nickel nitrate commonly crystallises with six water molecules, but can also be anhydrous, or with two, four or nine waters.Keith Lascelles, Lindsay G. Morgan, David Nicholls, Detmar Beyersmann, "Nickel Compounds" in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2005.

Triphenylphosphine oxide nickel nitrate [(C6H6)3PO]2Ni(NO3)2 is nonionic, with nitrato as a ligand. It can be made from nickel perchlorate. It is yellow and melts at 266 °C.

Nickel carbonate (NiCO3), hellyerite, crystallising with six water molecules, precipitates when an alkali bicarbonate is added to a Ni aqueous solution. Basic nickel carbonate, zaratite, with the formula Ni4CO3(OH)6(H2O)4, is produced when alkali carbonates are added to a nickel solution.

Nickel phosphate, Ni3(PO4)2 is also insoluble. A number of other phosphates have been made, including nanoporous substances resembling zeolites named with "Versailles Santa Barbara" or VSB. The nanoporous nickel phosphates can accommodate sufficiently small molecules and selectively catalyze reactions on them. A nickel arsenate (Ni3(AsO4)2·8H2O) occurs as the mineral annabergite.

The uranates include NiU2O6, NiUO4 α and β forms (orthorhombic a=6.415 Å; b=6.435 Å; c=6.835 Å), and NiU3O10.

Nickel perchlorate, Ni(ClO4)2, nickel chlorate, Ni(ClO3)2, nickel chromate (NiCrO4), nickel chromite (NiCr2O4), nickel(II) titanate, nickel bromate Ni(BrO3)2, nickel iodate (Ni(IO3)2), nickel stannate (NiSnO3) are some other oxyacid salts.

List formulanamemolstructcell Å°VZdensitycolourrefswtabcβÅ3g/cm3NiSO3nickel(II) sulfite hexahydratehexagonal8.7949.0026032.04emerald greenNiSO3nickel(II) sulfite trihydratelight greenNiSO3•3N2H4nickel(II) sulfite trihydrazine hydrateroseNiSO3•2N2H4nickel(II) sulfite dihydrazine hydrateblueNiS2O3•6H2ONickel(II) thiosulfate hexahydrate463.03orthorhombic9.28214.446.803912.142.03greendiaqua (4,4´-dimethylbipyridine- N,N´)(methanol) thiosulfato(S) nickel(II)triclinic8.1579.68511.714α=76.73 β=73.56 γ=78.23854.22aqua terpyridine(N,N´,N´´) thiosulfato(S,O) nickel(II) hemihydratemonoclinic,C2/c27.8669.27414.216114.24˚3350.8bis(dipyridylamine) thiosulfato(S,O) nickel(II) hemihydrateorthorhombic, Iba212.98616.82119.4794254.98NiS2O3(2,9-dimethyl-1,10-phenanthroline)(H2O)·H2O·CH3OHmonoclinic, C2/c26.2697.64118.38197.0036628NiS2O3(2,9-dimethyl-1,10-phenanthroline)monoclinic, P21/n11.10810.95511.666103.32˚1381.44Ni(NH2SO3)2Nickel(II) sulfamate tetrahydrate322.95triclinic P6.336.736.78α= 88.9 β=67.87 γ=67.76245.2712.19greenNi(SO3F)2nickel(II) fluorosulfateyellowNiSeO3anhydrous nickel(II) selenite742.68C2/c15.49159.935514.8416111.1732130.15324.630yellow brownNiSeO3anhydrous nickel(II) selenite742.68Orthorhombic5.88037.52354.9394218.52yellow green high pressureNiSeO3alpha nickel(II) selenite one third hydratetriclinic P8.13838.40348.5724α=123.713 β=90.174 γ=111.823435.8321.429citron yellowNiSeO3beta nickel(II) selenite one third hydratetriclinic P8.02228.21338.4364α=68.654 β=61.782 γ=66.363438.1121.422citron yellowNiSeO3nickel(II) selenite dihydratemonoclinic6.37828.77347.546781.451417.6143.524yellow brownNiSeO3nickel(II) selenite tetrahydratelight greenNiSe2O5anhydrous nickel(II) pyroselenitePnab Orthorhombic6075410.36626.7913427.7144.605light yellowNi12F2(SeO3)8(OH)6nickel hydroxo fluoro selenite, Dumortierite structurehexagonal P63mc12.7024.9221Ni12(SeO3)8(OH)8nickel hydroxy selenite, Dumortierite structure (basic nickel(II) selenite)hexagonal P63mc12.70044.9201687.281pale greenNiTeO3anhydrous nickel(II) telluriteOrthorhombic5.95647.49865.2128232.83yellow green high pressureNi3TeO6trinickel tellurate (nickel(II) orthotellurate)Hexagonal5.1035.10313.7814.272NiTe2O5nickel pyrotelluriteOrthorhombic8.8698.44112.1265.042Ni2Te3O8Monoclinic12.3925.20711.49698.65.702Ni6(TeO3)4(OH)4nickel hydroxy telluritehexagonal12.9934.9582light greenNi5Te4O12Cl2nickel tellurium oxychloride1066.585Monoclinic19.56745.245716.3084125.2891366.3845.186orangeNi5Te4O12Br2nickel tellurium oxybromide1155.77Monoclinic20.2555.249816.3005124.9371421.045.403orangeNi5Te4O12I2nickel tellurium oxyiodideMonoclinic20.7665.23016.464125.791451.14brownNi11(HPO3)8(OH)6nickel hydroxyphosphite (basic nickel(II) phosphite)hexagonal12.63294.9040677.771light greenNiMoO4•xH2Onickel(II) molybdate (hydrate)monoclinic11.9238.22014.007113.011264Ni(NO3)2nickel(II) nitrate dihydratetriclinic5.094657.104108.42881γ=78.698 β=102.7640 α=83.1985287.5Ni(NO3)2nickel(II) nitrate tetrahydratetriclinic7.57106.62316.26γ=97.26 β= 90.015 α=82.57802.3NiN2O2nickel(II) hyponitritelight greenNiP2O6nickel(II) hypophosphateorthorhombic Pnmm11.241818.52457.31881523.142.142Ni3(PO4)2nickel(II) phosphatemonoclinic10.10594.69645.827391.138276.5224.396greenish yellowα-Ni2P2O7alpha nickel(II) pyrophosphatemonoclinic6.91778.2758.974113.879469.744.12∃ α',β and δ formsNiHPO4nickel(II) hydrophosphatebeige yellow[Ni(PO3)2]3•xH2Onickel trimetaphosphate [Ni(PO3)2]4•xH2Onickel tetrametaphosphateNi2P4O12nickel cyclotetraphosphatemonoclinic C12/c111.6118.2189.826118.41824.74greenNi12H6(PO4)8(OH)6nickel hydroxy phosphate (basic nickel(II) phosphate)hexagonal12.46974.95311light green(H3O+NH4+)4[Ni18(HPO4)14(OH)3F9]•12H2ONanoporous nickel phosphate VSB-1hexagonal19.8345.03791710Ni20[(OH)12(H2O)6][(HPO4)8(PO4)4]•12H2ONanoporous nickel phosphate VSB-5hexagonal18.1536.3871827Ni3P6O18nickel hexametaphosphatetriclinic9.1099.26710.75113α=84.885 β=102.44 γ=101.64867.4pale greenNi3(AsO4)2·8H2OannabergiteMonoclinic10.17913.3094.7251052light greenNi12H6(AsO4)8(OH)6nickel hydroxy arsenate (basic nickel(II) arsenate)hexagonal12.6785.02591light greenNiAs2O4Nickel arseniteNi3(AsO4)2o-nickel orthoarsenate454.01orthorhombic5.94311.2638.164546.545.517Ni3(AsO4)2m-nickel orthoarsenate xanthiosite453.91monoclinic5.7649.55910.19492.95560.945.394golden yellowNi8.5As3O16Aerugite979.8trigonal5.951127.567281.915.772dark greenNiSb2O4Nickel metantimonitetetragonal8.63885.9052413.58(at 240K)NiSb2O6Nickel metantimonate(nickel antimony oxide)P42/mnm4.629579.19812Ni(H2O)6[Sb(OH)6]2bottinoite Nickel hexahydroantimonate(V)P316.0609.7922187.26pale blueNiTa2O6Nickel metatantalateP42/mnm4.715819.11632NiSn(SO3F)6nickel tin fluorosulfatelight yellowNi(SO3CF3)2nickel trifluoromethanesulfonateNiSn(SO3CF3)6nickel tin triflatelight yellow(Ni,Mg)10Ge3O16871.7trigonal R5.885028.6135286.115.060NiCO3anhydrous nickel(II) carbonate118.72rhombohedral4.611714.735271.3964.358Ni2SiO4nickel(II) orthosilicateliebenbergitenickel silicate olivineorthorhombic Pbnm4.72710.1205.911285.04Ni2GeO4nickel orthogermanatecubic Fd3m8.2218Ni(CN)2anhydrous nickel(II) cyanidetetragonal quad layer4.857012.8014NiB4O7γ-nickel(II) metadiborateP65224.25634.905547.56Ni(BrO4)2•6H2Onickel(II) perbromate hexahydrate454.61trigonal P7.8175.235277.912.725

References