# Nickel oxyacid salts

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. The heptahydrate crystallises from water below 31.5 above this blue hexhydrate forms, and above 53.3 the green form. Heating nickel sulfate dehydrates it, and then 700° 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 ends up producing nickel oxide and nickel sulfate.
Nickel thiosulfate NiS$_2$O$_3$ has the same structure as the magnesium salt. It has alternating layers of octahedral shaped nickel$^{2+}$ hexahydrate, and tetrahedral shaped S$_2$O$_3$$^{2−}$ perpendicular to the β direction. When heated to 90 °C it decomposes to form NiS. NiS$_2$O$_3$ can be made from BaS$_2$O$_3$ and NiSO$_4$. 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 NiSeO$_3$ has many different hydrates, anhydrous NiSeO$_3$ · 1⁄3 H$_2$O, NiSeO$_3$ · H$_2$O, NiSeO$_3$ · 2 H$_2$O (which is also a mineral called ahlfeldite), and NiSeO$_3$ · 4 H$_2$O.
Nickel nitrate commonly crystallises with six water molecules, but can also be anhydrous, or with two, four or nine waters. triphenylphosphine oxide nickel nitrate [(C$_6$H$_6$)$_3$PO]$_2$Ni(NO$_3$)$_2$ is non ionic, with nitrato as a ligand. It can be made from nickel perchlorate. It is yellow and melts at 266 °C.
Nickel carbonate NiCO$_3$ · 6 H$_2$O, 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 Ni$_4$CO$_3$(OH)$_6$(H$_2$O)$_4$, is produced when alkali carbonates are added to a nickel solution. Nickel phosphate, Ni$_3$(PO$_4$)$_2$ · 7 H$_2$O 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, Ni$_3$(AsO$_4$)$_2$·8H$_2$O occurs as the mineral annabergite.
Nickel perchlorate, Ni(ClO$_4$)$_2$ · 6 H$_2$O, nickel chlorate, Ni(ClO$_3$)$_2$ · 6 H$_2$O, nickel chromate (NiCrO$_4$), nickel chromite (NiCr$_2$O$_4$), nickel(II) titanate, nickel bromate Ni(BrO$_3$)$_2$ · 6 H$_2$O, nickel iodate (Ni(IO$_3$)$_2$ · 4 H$_2$O), nickel stannate (NiSnO$_3$ · 2 H$_2$O) are some other oxy-salts.
The uranates include NiU$_2$O$_6$, NiUO$_4$ α and β forms (orthorhombic a=6.415 Å; b=6.435 Å; c=6.835 Å), and NiU$_3$O$_{10.}$

## List

| formula | name | mol | struct | cell Å | cell Å | cell Å | ° | V | Z | density | colour |
| | | wt | | a | b | c | β | Å$^3$ | | g/cm$^3$ | |
| NiSO$_3$ · 6 H$_2$O | nickel(II) sulfite hexahydrate | | hexagonal | 8.794 | | 9.002 | | 603 | | 2.04 | emerald green |
| NiSO$_3$ · 3 H$_2$O | nickel(II) sulfite trihydrate | | | | | | | | | | light green |
| NiSO$_3$•3N$_2$H$_4$ · H$_2$O | nickel(II) sulfite trihydrazine hydrate | | | | | | | | | | rose |
| NiSO$_3$•2N$_2$H$_4$ · H$_2$O | nickel(II) sulfite dihydrazine hydrate | | | | | | | | | | blue |
| NiS$_2$O$_3$•6H$_2$O | Nickel(II) thiosulfate hexahydrate | 463.03 | orthorhombic | 9.282 | 14.44 | 6.803 | | 912.1 | 4 | 2.03 | green |
| | diaqua (4,4´-dimethylbipyridine- N,N´)(methanol) thiosulfato(S) nickel(II) | | triclinic | 8.157 | 9.685 | 11.714 | α=76.73 β=73.56 γ=78.23 | 854.2 | 2 | | |
| | aqua terpyridine(N,N´,N´´) thiosulfato(S,O) nickel(II) hemihydrate | | monoclinic,C2/c | 27.866 | 9.274 | 14.216 | 114.24˚ | 3350. | 8 | | |
| | bis(dipyridylamine) thiosulfato(S,O) nickel(II) hemihydrate | | orthorhombic, Iba2 | 12.986 | 16.821 | 19.479 | | 4254.9 | 8 | | |
| NiS$_2$O$_3$(2,9-dimethyl-1,10-phenanthroline)(H$_2$O)·H$_2$O·CH$_3$OH | | | monoclinic, C2/c | 26.269 | 7.641 | 18.381 | 97.00 | 3662 | 8 | | |
| NiS$_2$O$_3$(2,9-dimethyl-1,10-phenanthroline) | | | monoclinic, P21/n | 11.108 | 10.955 | 11.666 | 103.32˚ | 1381.4 | 4 | | |
| Ni(NH$_2$SO$_3$)$_2$ · 4 H$_2$O | Nickel(II) sulfamate tetrahydrate | 322.95 | triclinic P1 | 6.33 | 6.73 | 6.78 | α= 88.9 β=67.87 γ=67.76 | 245.27 | 1 | 2.19 | green |
| Ni(SO$_3$F)$_2$ | nickel(II) fluorosulfate | | | | | | | | | | yellow |
| NiSeO$_3$ | anhydrous nickel(II) selenite | 742.68 | C2/c | 15.4915 | 9.9355 | 14.8416 | 111.173 | 2130.15 | 32 | 4.630 | yellow brown |
| NiSeO$_3$ | anhydrous nickel(II) selenite | 742.68 | Orthorhombic | 5.8803 | 7.5235 | 4.9394 | | 218.52 | | | yellow green high pressure |
| NiSeO$_3$ · 1⁄3 H$_2$O | alpha nickel(II) selenite one third hydrate | | triclinic P1 | 8.1383 | 8.4034 | 8.5724 | α=123.713 β=90.174 γ=111.823 | 435.83 | 2 | 1.429 | citron yellow |
| NiSeO$_3$ · 1⁄3 H$_2$O | beta nickel(II) selenite one third hydrate | | triclinic P1 | 8.0222 | 8.2133 | 8.4364 | α=68.654 β=61.782 γ=66.363 | 438.11 | 2 | 1.422 | citron yellow |
| NiSeO$_3$ · 2 H$_2$O | nickel(II) selenite dihydrate | | monoclinic | 6.3782 | 8.7734 | 7.5467 | 81.451 | 417.61 | 4 | 3.524 | yellow brown |
| NiSeO$_3$ · 4 H$_2$O | nickel(II) selenite tetrahydrate | | | | | | | | | | light green |
| NiSe$_2$O$_5$ | anhydrous nickel(II) pyroselenite | | Pnab Orthorhombic | 60754 | 10.3662 | 6.7913 | | 427.71 | 4 | 4.605 | light yellow |
| Ni$_{12}$F$_2$(SeO$_3$)$_8$(OH)$_6$ | nickel hydroxo fluoro selenite, Dumortierite structure | | hexagonal P6$_3$mc | 12.702 | | 4.922 | | | 1 | | |
| Ni$_{12}$(SeO$_3$)$_8$(OH)$_8$ | nickel hydroxy selenite, Dumortierite structure (basic nickel(II) selenite) | | hexagonal P6$_3$mc | 12.7004 | | 4.9201 | | 687.28 | 1 | | pale green |
| NiTeO$_3$ | anhydrous nickel(II) tellurite | | Orthorhombic | 5.9564 | 7.4986 | 5.2128 | | 232.83 | | | yellow green high pressure |
| Ni$_3$TeO$_6$ | trinickel tellurate (nickel(II) orthotellurate) | | Hexagonal | 5.103 | 5.103 | 13.781 | | | | 4.272 | |
| NiTe$_2$O$_5$ | nickel pyrotellurite | | Orthorhombic | 8.869 | 8.441 | 12.126 | | | | 5.042 | |
| Ni$_2$Te$_3$O$_8$ | | | Monoclinic | 12.392 | 5.207 | 11.496 | 98.6 | | | 5.702 | |
| Ni$_6$(TeO$_3$)$_4$(OH)$_4$ | nickel hydroxy tellurite | | hexagonal | 12.993 | | 4.958 | | | 2 | | light green |
| Ni$_5$Te$_4$O$_{12}$Cl$_2$ | nickel tellurium oxychloride | 1066.585 | Monoclinic | 19.5674 | 5.2457 | 16.3084 | 125.289 | 1366.38 | 4 | 5.186 | orange |
| Ni$_5$Te$_4$O$_{12}$Br$_2$ | nickel tellurium oxybromide | 1155.77 | Monoclinic | 20.255 | 5.2498 | 16.3005 | 124.937 | 1421.0 | 4 | 5.403 | orange |
| Ni$_5$Te$_4$O$_{12}$I$_2$ | nickel tellurium oxyiodide | | Monoclinic | 20.766 | 5.230 | 16.464 | 125.79 | 1451.1 | 4 | | brown |
| Ni$_{11}$(HPO$_3$)$_8$(OH)$_6$ | nickel hydroxyphosphite (basic nickel(II) phosphite) | | hexagonal | 12.6329 | | 4.9040 | | 677.77 | 1 | | light green |
| NiMoO$_4$•xH$_2$O | nickel(II) molybdate (hydrate) | | monoclinic | 11.923 | 8.220 | 14.007 | 113.01 | 1264 | | | |
| Ni(NO$_3$)$_2$ · 2 H$_2$O | nickel(II) nitrate dihydrate | | triclinic | 5.09465 | 7.10410 | 8.42881 | γ=78.698 β=102.7640 α=83.1985 | 287.5 | | | |
| Ni(NO$_3$)$_2$ · 4 H$_2$O | nickel(II) nitrate tetrahydrate | | triclinic | 7.5710 | 6.623 | 16.26 | γ=97.26 β= 90.015 α=82.57 | 802.3 | | | |
| NiN$_2$O$_2$ | nickel(II) hyponitrite | | | | | | | | | | light green |
| NiP$_2$O$_6$ · 12 H$_2$O | nickel(II) hypophosphate | | orthorhombic Pnmm | 11.2418 | 18.5245 | 7.3188 | | 1523.1 | 4 | 2.142 | |
| Ni$_3$(PO$_4$)$_2$ | nickel(II) phosphate | | monoclinic | 10.1059 | 4.6964 | 5.8273 | 91.138 | 276.52 | 2 | 4.396 | greenish yellow |
| α-Ni$_2$P$_2$O$_7$ | alpha nickel(II) pyrophosphate | | monoclinic | 6.9177 | 8.275 | 8.974 | 113.879 | 469.7 | 4 | 4.12 | ∃ α',β and δ forms |
| NiHPO$_4$ | nickel(II) hydrophosphate | | | | | | | | | | beige yellow |
| [Ni(PO$_3$)$_2$]$_3$•xH$_2$O | nickel trimetaphosphate | | | | | | | | | | |
| [Ni(PO$_3$)$_2$]$_4$•xH$_2$O | nickel tetrametaphosphate | | | | | | | | | | |
| Ni$_2$P$_4$O$_{12}$ | nickel cyclotetraphosphate | | monoclinic C12/c1 | 11.611 | 8.218 | 9.826 | 118.41 | 824.7 | 4 | | green |
| Ni$_{12}$H$_6$(PO$_4$)$_8$(OH)$_6$ | nickel hydroxy phosphate (basic nickel(II) phosphate) | | hexagonal | 12.4697 | | 4.9531 | | | 1 | | light green |
| (H$_3$O$^+$NH$_4$$^+$)$_4$[Ni$_{18}$(HPO$_4$)$_{14}$(OH)$_3$F$_9$]•12H$_2$O | Nanoporous nickel phosphate VSB-1 | | hexagonal | 19.834 | | 5.0379 | | 1710 | | | |
| Ni$_{20}$[(OH)$_{12}$(H$_2$O)$_6$][(HPO$_4$)$_8$(PO$_4$)$_4$]•12H$_2$O | Nanoporous nickel phosphate VSB-5 | | hexagonal | 18.153 | | 6.387 | | 1827 | | | |
| Ni$_3$P$_6$O$_{18}$ · 17 H$_2$O | nickel hexametaphosphate | | triclinic | 9.109 | 9.267 | 10.75113 | α=84.885 β=102.44 γ=101.64 | 867.4 | | | pale green |
| Ni$_3$(AsO$_4$)$_2$·8H$_2$O | annabergite | | Monoclinic | 10.179 | 13.309 | 4.725 | 105 | | 2 | | light green |
| Ni$_{12}$H$_6$(AsO$_4$)$_8$(OH)$_6$ | nickel hydroxy arsenate (basic nickel(II) arsenate) | | hexagonal | 12.678 | | 5.0259 | | | 1 | | light green |
| NiAs$_2$O$_4$ | Nickel arsenite | | | | | | | | | | |
| Ni$_3$(AsO$_4$)$_2$ | o-nickel orthoarsenate | 454.01 | orthorhombic | 5.943 | 11.263 | 8.164 | | 546.5 | 4 | 5.517 | |
| Ni$_3$(AsO$_4$)$_2$ | m-nickel orthoarsenate xanthiosite | 453.91 | monoclinic | 5.764 | 9.559 | 10.194 | 92.95 | 560.9 | 4 | 5.394 | golden yellow |
| Ni$_{8.5}$As$_3$O$_{16}$ | Aerugite | 979.8 | trigonal | 5.9511 | | 27.567 | | 281.9 | 1 | 5.772 | dark green |
| NiSb$_2$O$_4$ | Nickel metantimonite | | tetragonal | 8.6388 | | 5.9052 | | 413.58 | | (at 240K) | |
| NiSb$_2$O$_6$ | Nickel metantimonate (nickel antimony oxide) | | P4$_2$/mnm | 4.62957 | | 9.1981 | | | 2 | | |
| Ni(H$_2$O)$_6$[Sb(OH)$_6$]$_2$ | bottinoite Nickel hexahydroantimonate(V) | | P3 | 16.060 | | 9.792 | | 2187.2 | 6 | | pale blue |
| NiTa$_2$O$_6$ | Nickel metatantalate | | P4$_2$/mnm | 4.71581 | | 9.1163 | | | 2 | | |
| NiSn(SO$_3$F)$_6$ | nickel tin fluorosulfate | | | | | | | | | | light yellow |
| Ni(SO$_3$CF$_3$)$_2$ | nickel trifluoromethanesulfonate | | | | | | | | | | |
| NiSn(SO$_3$CF$_3$)$_6$ | nickel tin triflate | | | | | | | | | | light yellow |
| (Ni,Mg)$_{10}$Ge$_3$O$_{16}$ | | 871.7 | trigonal R3 | 5.8850 | | 28.6135 | | 286.1 | 1 | 5.060 | |
| NiCO$_3$ | anhydrous nickel(II) carbonate | 118.72 | rhombohedral | 4.6117 | | 14.735 | | 271.39 | 6 | 4.358 | |
| Ni$_2$SiO$_4$ | nickel(II) orthosilicate liebenbergite nickel silicate olivine | | orthorhombic Pbnm | 4.727 | 10.120 | 5.911 | | 285.0 | 4 | | |
| Ni$_2$GeO$_4$ | nickel orthogermanate | | cubic Fd3m | 8.221 | | | | | 8 | | |
| Ni(CN)$_2$ | anhydrous nickel(II) cyanide | | tetragonal quad layer | 4.8570 | | 12.801 | | | 4 | | |
| NiB$_4$O$_7$ | γ-nickel(II) metadiborate | | P6$_5$22 | 4.256 | | 34.905 | | 547.5 | 6 | | |
| Ni(BrO$_4$)$_2$•6H$_2$O | nickel(II) perbromate hexahydrate | 454.61 | trigonal P3 | 7.817 | | 5.235 | | 277.9 | 1 | 2.725 | |