# Nickel double salts

Nickel is one of the metals that can form Tutton's salts. The singly charged ion can be any of the full range of potassium, rubidium, cesium, ammonium (${\ce {NH4}}$), or thallium. As a mineral the ammonium nickel salt, (NH$_4$)$_2$Ni(SO$_4$)$_2$ · 6 H$_2$O, can be called nickelboussingaultite. With sodium, the double sulfate is nickelblödite Na$_2$Ni(SO$_4$)$_2$ · 4 H$_2$O from the blödite family. Nickel can be substituted by other divalent metals of similar sized to make mixtures that crystallise in the same form.
Nickel forms double salts with Tutton's salt structure with tetrafluoroberyllate with the range of cations of ammonia, potassium, rubidium, cesium, and thallium.
Anhydrous salts of the formula M$_2$Ni$_2$(SO$_4$)$_3$, which can be termed metal nickel trisulfates, belong to the family of langbeinites. The known salts include (NH$_4$)$_2$Ni$_2$(SO$_4$)$_3$, K$_2$Ni$_2$(SO$_4$)$_3$ and Rb$_2$Ni$_2$(SO$_4$)$_3$, and those of Tl and Cs are predicted to exist.
Some minerals are double salts, for example Nickelzippeite Ni$_2$(UO$_2$)$_6$(SO$_4$)$_3$(OH)$_{10}$ · 16H$_2$O which is isomorphic to cobaltzippeite, magnesiozippeite and zinczippeite, part of the zippeite group.
Double hydrides of nickel exist, such as Mg$_2$NiH$_4$.
| formula | name | mol | struct | cell Å | cell Å | cell Å | ° | V | Z | density | colour |
| | | wt | | a | b | c | β | Å$^3$ | | g/cm$^3$ | |
| Li$_2$[NiF(PO$_4$)] | Lithium nickel fluorophosphate | 186.56 | orthorhombic | 10.473 | 6.289 | 10.846 | | 714.3 | 8 | 3.469 | |
| Na$_2$[NiF(PO$_4$)] | sodium nickel fluorophosphate | 218.645 | Pbcn | | | | 90 | 823.4 | | | |
| Na$_2$Ni(SO$_4$)$_2$ · 4 H$_2$O | nickelblödite | 368.867 | monoclinic | 11.045 | 8.193 | 5.535 | 100.50 | | | 2.487 | green |
| K$_2$Ni$_2$(SO$_4$)$_3$ | potassium nickel trisulfate | 483.77 | orthorhombic | 9.8436 | 9.8436 | 9.8436 | 90 | | | 3.369 | |
| Rb$_2$Ni$_2$(SO$_4$)$_3$ | rubidium nickel trisulfate | 576.51 | | 9.9217 | 9.9217 | 9.9217 | 90 | | | 3.921 | |
| (NH$_4$)$_2$Ni$_2$(SO$_4$)$_3$ | ammonium nickel trisulfate | 441.65 | orthorhombic | 9.904 | 9.904 | 9.904 | 90 | | | 3.02 | |
| (NH$_4$)$_4$Ni$_3$(SO$_4$)$_5$ | ammonium nickel pentasulfate | 728.56 | | | | | | | | | yellow |
| NiLa(SeO$_3$)$_2$Cl | nickel lanthanum diselenite chloride | 486.977 | hexagonal | 8.666 | | 18.662 | | 1194.2 | 6 | | (153K) |
| NiNd$_{10}$(SeO$_3$)$_{12}$Cl$_8$ | nickel Neodymium diselenite chloride | | monoclinic | 15.8175 | 1578,68 | 19.276 | 114.202 | 7407 | 4 | | (153K) |
| Ni$_6$Fe$^{3+}$$_2$(SO$_4$)(OH)$_{16}$ · 4 H$_2$O | honessite | 904.08 | trigonal | 3.083 | | 26.71 | | 219.86 | 0.25 | 1.71 | green |
| NiTi(SO$_4$)$_3$ | nickel titanium sulfate | | monoclinic | 8.254 | 8.54 | 14.1444 | 124.967 | 817 | 4 | 3.21 | |
| Na$_2$Ni(SeO$_4$)$_2$ · 2 H$_2$O | sodium nickel selenate dihydrate | | triclinic | 5.507 | 5.905 | 7.172 | α = 108.56 °, β = 99.07 °, γ = 106.35 ° | 204.2 | 1 | | |
| K$_2$Ni(SeO$_4$)$_2$ · 2 H$_2$O | potassium nickel selenate dihydrate | | | | | | | | | | |
| K$_2$Ni(SeO$_4$)$_2$ · 6 H$_2$O | potassium nickel selenate Tuttons salt | 527.52 | monoclinic | a | b | c | 104.45 | | 4 | 2.559 | bright green |
| Rb$_2$Ni(SeO$_4$)$_2$ · 6 H$_2$O | rubidium nickel selenate Tuttons salt | 619.62 | monoclinic | a | b | c | 105.20 | | 4 | 2.856 | bright green |
| Cs$_2$Ni(SeO$_4$)$_2$ · 6 H$_2$O | caesium nickel selenate Tuttons salt | 713.62 | monoclinic | 9.426 | 12.961 | 6.473 | 106.17 | 759.5 | 2 | 3.114 | bright emerald green |
| (NH$_4$)$_2$Ni(SeO$_4$)$_2$ · 6 H$_2$O | ammonium nickel selenate Tuttons salt | 485.68 | monoclinic | a | b | c | 106.29 | | 4 | 2.243 | bright green |
| Tl$_2$Ni(SeO$_4$)$_2$ · 6 H$_2$O | thallium nickel selenate Tuttons salt | | monoclinic | a | b | c | 105.60 | | 4 | 3.993 | bright green |
| K$_2$NiP$_2$O$_7$ | | 310.85 | monoclinic P2$_1$ | 9.230 | 17.540 | 8.32 | 91.44 | 1346.3 | 8 | 3.067 | |
| K$_6$Sr$_2$Ni$_5$(P$_2$O$_7$)$_5$ | | 786.55 | monoclinic P2$_1$/c | 11.038 | 9.53 | 7.438 | 100.13 | 1578 | 2 | 3.309 | yellow |
| NaNi$_2$(SO$_4$)$_2$[(H$_2$O)(OH)] | | | monoclinic C2/m Natrochalcite-type | 8.605 | 6.185 | 7.336 | 114.78 | 354.5 | 2 | | |
| BaNi$_2$(PO$_4$)$_2$ | barium nickel phosphate | | Trigonal R-3 | 4.8112 | 4.8112 | 23.302 | | 467.1 | 3 | | green |
| BaNi$_2$(AsO$_4$)$_2$ | barium nickel arsenate | | Trigonal R-3 | 4.945 | 4.945 | 23.61 | | 532.59 | 3 | 5.31 | |
| BaNi$_2$(VO$_4$)$_2$ | barium nickel vanadate | | Trigonal R-3 | 5.0375 | 5.0375 | 22.33 | | | 3 | | |
| Na$_4$Ni$_7$(AsO$_4$)$_6$ | tetrasodium heptanickel hexaarsenate | 1336.3 | monoclinic C2/m | 14.538 | 14.505 | 10.6120 | 118.299 | 1970.3 | 4 | | brown |
| K$_2$Ni(CO$_3$)$_2$ · H$_2$O | potassium nickel carbonate Potassium tetraaquadicarbonatonickelate | | monoclinic Baylissite-type | 6.755 | 6.156 | 12.2406 | 113.265 | 467.6 | 2 | 2.34 | |
| Rb$_2$Ni(CO$_3$)$_2$ · H$_2$O | Rubidium nickel carbonate | | monoclinic Baylissite-type | 6.971 | 6.348 | 12.2807 | 114.289 | 495.34 | 2 | 2.83 | |
| NiTh(NO$_3$)$_6$ · 8 H$_2$O | nickel thorium nitrate | | Monoclinic P2$_1$/c | 9.089 | 8.728 | 13.565 | 96.65 | 1068.8(2) | | | |
| K[NiGa$_2$(PO$_4$)$_3$(H$_2$O)$_2$] | Potassium nickel(II) gallium phosphate hydrate | 558.17 | Monoclinic C2/c | 13.209 | 10.173 | 8.813 | 107.68 | 1128.4 | Z = 4 | | |
| KNi$_3$(PO$_4$)P$_2$O$_7$ | Potassium trinickel(II) orthophosphate diphosphate | 484.14 | Monoclinic | 9.8591 | 9.3953 | 9.9778 | 118.965 | 808.63 | 4 | | |
| KNiPO$_4$ | potassium nickel phosphate | | | | | | | | | | |
| KNiPO$_4$ · 6 H$_2$O | potassium nickel phosphate hexahydrate | | monoclinic P2$_1$ | 6.8309 | 11.0610 | 6.1165 | 91.045 | 462.07 | 2 | | |
| NiK$_4$(P$_3$O$_9$)$_2$ · 7 H$_2$O | nickel potassium tricyclophosphate hydrate | | orthorhombic Fm2m | 23.03 | 11.882 | 8.732 | | | 4 | | blue |
| NiK$_4$(P$_3$O$_9$)$_2$ | nickel potassium tricyclophosphate | | triclinic P-1 | 6.143 | 6.80 | 12.80 | α=102.8 β=89.7 γ=66.03 | 473.56 | 1 | | |
| NaK$_5$Ni$_5$(P$_2$O$_7$)$_4$ | Sodium pentapotassium pentanickel tetra(diphosphate) | 1207.80 | triclinic | 7.188 | 9.282 | 10.026(5) | α=109.31 β=90.02 γ=104.07 | 610.0 | 1 | | |
| NH$_4$NiPO$_4$·H$_2$O | ammonium nickel phosphate hydrate | | orthorhombic | 5.566 | 8.760 | 4.742 | | 231.2 | | | |
| NH$_4$NiPO$_4$·6H$_2$O | ammonium nickel phosphate hydrate Ni-struvite | | Orthorhombic Pmn2$_1$ | 6.924 | 6.104 | 11.166 | | 471.5 | 2 | | |
| LiNiPO$_4$ | lithium nickel phosphate | | orthorhombic | 10.032 | 5.855 | 4.681 | | 274.9 | 4 | | brown |
| NaNiPO$_4$ | sodium nickel phosphate | | Pnma maricite structure | 8.7839 | 6.7426 | 5.0368 | | 298.31 | 4 | | yellow |
| NaNiPO$_4$ | sodium nickel phosphate | | Pnma triphylite form | 4.98 | 6.13 | 9.98 | | 304.23 | | | |
| Na$_4$Ni$_7$(PO$_4$)$_6$ | | | Cm | 10.550 | 13.985 | 6.398 | 104.87 | 912.4 | 2 | 3.906 | |
| NaNiPO$_4$ · 7 H$_2$O | sodium nickel phosphate heptahydrate | | tetrahedral P4$_2$/mmc | 6.7390 | | 10.9690 | | 498.15 | 2 | | |
| Na$_3$NiP$_3$O$_{10}$ · 12 H$_2$O | trisodium nickel triphosphate dodecahydrate | | monoclinic (pseudoorthorhombic) | 15.0236 | 9.1972 | 14.6654. | 90.0492 | 2014.46 | | 1.967 | light green |
| Na$_5$Ni$_2$(PO$_4$)$_3$ · H$_2$O | Pentasodium dinickel triphosphate hydrate | | monoclinic space group P2$_1$/n | 14.0395 | 5.185 | 16.4739 | 110.419 | | | | |
| Na$_6$Ni$_2$(PO$_4$)$_3$OH | | | orthorhombic Pcmb | 7.501 | 21.4661 | 7.173 | | | | | |
| Na$_2$Ni$_3$(OH)$_2$(PO$_4$)$_2$ | sodium nickel hydroxide phosphate | | monoclinic | 14.259 | 5.695 | 4.933 | 104.28 | | 2 | 3.816 | |
| NiNa$_4$(P$_3$O$_9$)$_2$ · 6 H$_2$O | nickel tetrasodium cyclotriphosphate hexahydrate | | triclinic | 6.157 | 6.820 | 10.918 | α=80.21 β=97.8 γ=119.5 | 409.8 | 1 | | |
| NiRb$_4$(P$_3$O$_9$)$_2$ | nickel tetrarubidium cyclotriphosphate | | P-31c | 7.288 | 7.288 | 20.343 | | | 2 | | |
| NiCs$_4$(P$_3$O$_9$)$_2$ · 6 H$_2$O | nickel tetracaesium cyclotriphosphate hydrate | | orthorhombic | 19.992 | 6.500 | 18.445 | | | 4 | | |
| NiCs$_4$(PO$_3$)$_6$ | nickel tetracaesium cyclotriphosphate | | rhombohedral P-3$_1$c | 11.602 | 11.602 | 9.078 | | 1058.24 | 2 | | |
| NiAg$_4$(P$_3$O$_9$)$_2$ · 6 H$_2$O | nickel tetrasilver cyclotriphosphate hexahydrate | | triclinic | 9.209 | 8.053 | 6.841 | α=89.15 β=102.94 γ=97.24 | | 1 | | |
| NiAg$_4$(P$_3$O$_9$)$_2$ | nickel tetrasilver cyclotriphosphate | | triclinic | 6.100 | 6.783 | 10.764 | α = 78.66 β=96.85 γ=113.36 | 401 | 1 | | |
| Ni(NH$_4$)$_4$(P$_3$O$_9$)$_2$ · 4 H$_2$O | nickel tetraammonium cyclotriphosphate tetrahydrate | | monoclinic | | | | | | 2 | | |
| TlNi$_4$(PO$_4$)$_3$ | Thallium nickel triphosphate | | orthorhombic Cmc2$_1$ | | | | | | 4 | | pale yellow |
| Tl$_4$Ni$_6$(PO$_4$)$_6$ | Thallium nickel hexaphosphate | | monoclinic Cm | | | | | | 4 | | yellow brown |
| Tl$_2$Ni$_4$P$_2$O$_7$(PO$_4$)$_2$ | | | monoclinic C2/c | | | | | | 8 | | brown |
| NiMnSb | Nickel manganese antimonide | | cubic | 5.945 | | | | 210.1 | 4 | 7.57 | |
| NiMnSi | Nickel manganese silicide | | Orthorhombic | 5.8967 | 3.6124 | 6.9162 | | 147.32 | 4 | | |
| NiMnGe | | | orthorhombic Pnma | 6.053 | 3.769 | 7.090 | | 161.75 | 2 | | |
| NiFeGe | | | hexagonal | | | | | | | | |
| TiNiSi | | | orthorhombic | | | | | | | | |
| NaNiIO$_6$ | sodium nickel periodate | | orthorhombic | 8.599 | 2.492 | 10.281 | | 220.3 | | | |
| KNiIO$_6$ | potassium nickel periodate | | orthorhombic | 12.09 | 3.683 | 6.062 | | 269.9 | | | |
| KNiIO$_6$ | potassium nickel periodate | | triclinic | 6.4203 | 5.075 | 4.223 | α= 65.07 β= 92.717 γ=109.95 | 116.51 | | | |
Double fluorides include the above-mentioned fluoroanion salts, and those fluoronickelates such as NiF$_4$ and NiF$_6$. Other odd ones include an apple green coloured KNiF$_3$·H$_2$O and NaNiF$_3$·H$_2$O, aluminium nickel pentafluoride AlNiF$_5$·7H$_2$O, ceric nickelous decafluoride Ce$_2$NiF$_{10}$·7H$_2$O, niobium nickel fluoride Ni$_3$H$_4$Nb$_2$F$_{20}$·19H$_2$O, vanadium nickel pentafluoride VNiF$_5$·7H$_2$O, vanadyl nickel tetrafluoride VONiF$_4$·7H$_2$O, chromic nickelous pentafluoride CrNiF$_5$·7H$_2$O, molybdenum nickel dioxytetrafluoride NiMoO$_2$F$_4$·6H$_2$O, tungsten nickel dioxytetrafluoride NiWO$_2$F$_4$·6H$_2$O and NiWO$_2$F$_4$·10H$_2$O, manganic nickel pentafluoride MnNiF$_4$·7H$_2$O, nickelous ferric fluoride FeNiF$_5$·7H$_2$O.
Nickel trichloride double salts exist which are polymers. Nickel is in octahedral coordination, with double halogen bridges. Examples of this include RbNiCl$_3$, pinkish tan coloured H$_2$NN(CH$_3$)$_3$NiCl$_3$. Other double trichlorides include potassium nickel trichloride KNiCl$_3$·5H$_2$O, yellow cesium nickel trichloride CsNiCl$_3$, lithium nickel trichloride LiNiCl$_3$·3H$_2$O, hyrdrazinium nickel tetrachloride, and nickel ammonium chloride hexahydrate NH$_4$NiCl$_3$·6H$_2$O.
The tetrachloronickelates contain a tetrahedral NiCl$_4$$^{2−}$ and are dark blue. Some salts of organic bases are ionic liquids at standard conditions. tetramethylammonium nickel trichloride is pink and very insoluble. Other tetrachlorides include rubidium nickel tetrachloride, lithium nickel tetrachloride Li$_2$NiCl$_4$·4H$_2$O stable from 23 to 60°, stannous nickel tetrachloride ${\ce {SnCl2.NiCl2.6H2O}}$, stannic nickel hexachloride ${\ce {SnCl4.NiCl2.6H2O}}$ is tetragonal.
Lithium nickel hexachloride Li$_4$NiCl$_6$·10H$_2$O is stable from 0 to 23°.
Copper nickel dioxychloride 2CuO·NiCl$_2$·6H$_2$O, and copper nickel trioxychloride 3CuO·NiCl$_2$·4H$_2$O.
Cadmium dinickel hexachloride, ${\ce {CdCl2.2NiCl2.12H2O}}$ crystallises in hexagonal system, dicadmium dinickel hexachloride, ${\ce {2CdCl2.NiCl2.12H2O}}$ has rhombic crystals, and is pleochroic varying from light to dark green.
Thallic nickel octochloride ${\ce {2TlCl3.NiCl2.8H2O}}$ is bright green.
Double bromides include the tetrabromonickelates, and also caesium nickel tribromide, CsNiBr$_3$ copper nickel trioxybromide, 3CuO·NiBr$_2$·4H$_2$O mercuric nickel bromide, Hg$_2$NiBr6, HgNiBr$_4$. Aqueous nickel bromide reacting with mercuric oxide yields mercuric nickel oxybromide, ${\ce {6NiO.NiBr2.HgBr2.20H2O}}$ didymium nickel bromide, ${\ce {2(Pr,Nd)Br3.3NiBr2.18H2O}}$ is reddish brown (mixture of praseodymium and neodymium) Lanthanum nickel bromide, ${\ce {2LaBr3.3NiBr2.18H2O}}$ nickel stannic bromide (or nickel bromostannate) NiSnBr$_6$·8H$_2$O is apple green.
The tetraiodonickelates are blood red coloured salts of the NiI$_4$ ion with large cations. Double iodides known include mercuric nickel hexaiodide 2HgI$_2$•NiI$_2$ · 6 H$_2$O, mercuric nickel tetraiodide HgI$_2$•NiI$_2$ · 6 H$_2$O, and lead nickel hexaiodide I$_2$•2NiI$_2$ · 3 H$_2$O.
The diperiodatonickelates of nickel IV are strong oxidisers, and akali monoperiodatonickelates also are known.
Nickel forms double nitrates with the lighter rare earth elements. The solid crystals have the formula ${\ce {Ni3Me2(NO3)12.24H2O}}$. The metals include La Ce Pr Nd Sm Gd and the non rare earth Bi. Nickel can also be replaced by similar divalent ions, Mg, Mn Co Zn. For the nickel salts melting temperatures range from 110.5° for La, 108.5° for Ce, 108° for Pr, 105.6° for Nd, 92.2° for Sm and down to 72.5° for Gd The Bi salt melting at 69°. Crystal structure is hexagonal with Z=3. ${\ce {Ni3La2(NO3)12.24H2O}}$ becomes ferromagnetic below 0.393 K. These double nickel nitrates have been used to separate the rare earth elements by fractional crystallization.
Nickel thorium nitrate has formula NiTh(NO$_3$)$_6$ · 8 H$_2$O. Nickel atoms can be substituted by other ions with radius 0.69 to 0.83 Å. The nitrates are coordinated on the thorium atom and the water to the nickel. Enthalp of solution of the octahydrate is 7 kJ/mol. Enthalpy of formation is -4360 kJ/mol. At 109° the octahydrate becomes ${\ce {NiTh(NO3)6.6H2O}}$, and at 190° ${\ce {NiTh(NO3)6.3H2O}}$ and anhydrous at 215°. The hexahydrate has Pa3 cubic structure.
Various double amides containing nickel clusters have been made using liquid ammonia as a solvent. Substances made include red Li$_3$Ni$_4$(NH$_2$)$_{11}$·NH$_3$ (Pna21; Z = 4; a = 16.344(3) Å; b = 12.310(2) Å; c = 8.113(2) Å v=1631 D=1.942), and Cs$_2$Ni(NH$_2$)$_4$•NH$_3$ (P21/c; Z = 4; a =9.553(3) Å; b = 8.734(3) Å; c = 14.243(3) Å; β = 129.96(3)° V=910 D=2.960). These are called amidonickel compounds. Yet others include Li$_4$Ni$_4$(NH$_2$)$_{12}$·NH$_3$, Na$_2$Ni(NH$_2$)$_4$, orange red Na$_2$Ni(NH$_2$)$_4$•2NH$_3$, Na$_2$Ni(NH$_2$)$_4$•NH$_3$, K$_2$Ni(NH$_2$)$_4$•0.23KNH$_2$, and Rb$_2$Ni(NH$_2$)$_4$•0.23RbNH$_2$.
Nickel dihydrogen phosphide (Ni(PH$_2$)$_2$) can form orange, green or black double salts KNi(PH$_2$)$_3$) that crystallise from liquid ammonia. They are unstable above -78 °C, giving off ammonia, phosphine and hydrogen.