Nickel double salts

Tutton's 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, or thallium.

Mineral forms

As a mineral the ammonium nickel salt, ₂Ni₂, can be called nickelboussingaultite. With sodium, the double sulfate is nickelblödite Na₂Ni₂ from the blödite family. Nickel can be substituted by other divalent metals of similar sized to make mixtures that crystallise in the same form.

Langbeinites

Anhydrous salts of the formula M₂Ni₂₃, which can be termed metal nickel trisulfates, belong to the family of langbeinites. The known salts include ₂Ni₂₃, K₂Ni₂₃ and Rb₂Ni₂₃, and those of Tl and Cs are predicted to exist.

Double halides

Fluorides

Double fluorides include the fluoroanion salts, and those fluoronickelates such as NiF₄ and NiF₆:

KNiF₃·H₂O and NaNiF₃·H₂O – apple green coloured
aluminium nickel pentafluoride
ceric nickelous decafluoride
niobium nickel fluoride
vanadium nickel pentafluoride
vanadyl nickel tetrafluoride
chromic nickelous pentafluoride
molybdenum nickel dioxytetrafluoride
tungsten nickel dioxytetrafluoride hexahydrate and decahydrate
manganic nickel pentafluoride
nickelous ferric fluoride

Chlorides

Trichlorides

Nickel trichloride double salts exist which are polymers. Nickel is in octahedral coordination, with double halogen bridges. Examples of this include RbNiCl₃, pinkish tan coloured H₂NN₃NiCl₃.
Other double trichlorides include:

potassium nickel trichloride
yellow cesium nickel trichloride
lithium nickel trichloride
nickel ammonium chloride hexahydrate

Tetrachlorides

The tetrachloronickelates contain a tetrahedral NiCl₄²⁻ 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:

hyrdrazinium nickel tetrachloride
lithium nickel tetrachloride – stable from 23 to 60°
rubidium nickel tetrachloride
stannous nickel tetrachloride

Hexachlorides

Double hexachlorides include:

cadmium dinickel hexachloride – crystallises in hexagonal system
dicadmium dinickel hexachloride – rhombic crystals, pleochroic varying from light to dark green.
lithium nickel hexachloride Li₄NiCl₆·10H₂O – stable from 0 to 23°
stannic nickel hexachloride – tetragonal

Octochlorides

Thallic nickel octochloride 2TlCl₃·NiCl₂·8H₂O is bright green.

Oxychlorides

Copper nickel dioxychloride 2CuO·NiCl₂·6H₂O and copper nickel trioxychloride 3CuO·NiCl₂·4H₂O exist.

Bromides

Double bromides include the tetrabromonickelates. Other salts include:

caesium nickel tribromide
copper nickel trioxybromide
didymium nickel bromide – reddish brown, mixture of praseodymium and neodymium
lanthanum nickel bromide
mercuric nickel bromides and
mercuric nickel oxybromide – prepared by reacting nickel bromide with mercuric oxide
nickel stannic bromide or nickel bromostannate – apple green

Iodides

The tetraiodonickelates are blood-red coloured salts of the NiI₄ ion with large cations. The diperiodatonickelates of nickel are strong oxidisers, and akali monoperiodatonickelates also are known.
Double iodides include:

mercuric nickel hexaiodide
mercuric nickel tetraiodide
lead nickel hexaiodide

Double nitrates

Lanthanides

Nickel forms double nitrates with the lighter rare-earth elements. The solid crystals have the formula Ni₃Me₂₁₂•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, and 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. Ni₃La₂₁₂•24H₂O becomes ferromagnetic below 0.393 K. These double nickel nitrates have been used to separate the rare earth elements by fractional crystallization.

Actinides

Nickel thorium nitrate has formula NiTh₆. 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. Enthalpy of solution of the octahydrate is 7 kJ/mol. Enthalpy of formation is -4360 kJ/mol. At 109° the octahydrate becomes NiTh₆•6H₂O, and at 190° NiTh₆•3H₂O and anhydrous at 215°.
The hexahydrate has Pa cubic structure.

Double amides

Various double amides containing nickel clusters have been made using liquid ammonia as a solvent. These are called amidonickel compounds.
These include:

Li₃Ni₄₁₁·NH₃ Å; b = 12.310 Å; c = 8.113 – red
Li₄Ni₄₁₂·NH₃, Na₂Ni₄
Na₂Ni₄•NH₃
Na₂Ni₄•2NH₃ – orange red
K₂Ni₄•0.23KNH₂
Rb₂Ni₄•0.23RbNH₂
Cs₂Ni₄•NH₃ Å; b = 8.734 Å; c = 14.243 Å; β = 129.96

Double hydrides

Double hydrides of nickel exist, such as Mg₂NiH₄.

Double dihydrogen phosphides

Nickel dihydrogen phosphide can form orange, green or black double salts KNi that crystallise from liquid ammonia. They are unstable above -78 °C, giving off ammonia, phosphine and hydrogen.

Double tetrafluoroberyllates

Nickel forms double salts with Tutton's salt structure with tetrafluoroberyllate and a range of cations including ammonia, potassium, rubidium, cesium, and thallium.

Other minerals

Some minerals are double salts, for example nickelzippeite Ni₂₆₃₁₀ · 16H₂O which is isomorphic to cobaltzippeite, magnesiozippeite and zinczippeite, part of the zippeite group.