Nickel forms a series of mixed oxide compounds which are commonly called nickelates. A nickelate is an anion containing nickel or a salt containing a nickelate anion, or a double compound containing nickel bound to oxygen and other elements. Nickel can be in different or even mixed oxidation states, ranging from +1, +2, +3 to +4. The anions can contain a single nickel ion, or multiple to form a cluster ion. The solid mixed oxide compounds are often ceramics, but can also be metallic. They have a variety of electrical and magnetic properties. Rare-earth elements form a range of perovskite nickelates, in which the properties vary systematically as the rare-earth element changes. Fine tuning of properties is achievable with mixtures of elements, applying stress or pressure, or varying the physical form. Inorganic chemists call many compounds that contain nickel centred anions "nickelates". These include the

chloronickelate Tetrachloronickelate is the metal complex with the formula iCl4sup>2−. Salts of the complex are available with a variety of cations, but a common one is tetraethylammonium. When concentrated lithium chloride and nickel chloride solution in wa ...

s, fluoronickelates,

tetrabromonickelate The tetrabromonickelate anion contains a doubly-charged nickel atom (Ni2+) surrounded by four bromide ions in a tetrahedral arrangement. The formula is iBr4sup>2−. The anion combines with cations to form a series of salts called tetrabromonicke ...

tetraiodonickelate Tetraiodonickelate is a complex ion of nickel with four iodide atoms iI4− arranged in a tetrahedron. iI4− is red in solution. This colour is due to absorption around 530 nm and below 450 nm. Maximum light transmission is aroun ...

s, cyanonickelates, nitronickelates and other nickel-organic acid complexes such as

oxalatonickelate The oxalatonickelates are a class of compounds that contain nickel complexed by oxalate groups. They form a series of double salts, and include clusters with multiple nickel atoms. Since oxalate functions as a bidentate ligand it can satisfy t ...

Alkali nickelates

The lithium nickelates are of interest to researchers as cathodes in lithium cells, as these substance can hold a variable amount of lithium, with the nickel varying in oxidation state.

Rare-earth nickelates

Rare-earth nickelates with nickel in a +1 oxidation state have an electronic configuration to same as for cuprates and so are of interest to high-temperature superconductor researchers. Other rare-earth nickelates can function as

fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...

catalysts. The ability to switch between an insulating and a conducting state in some of these materials is of interest in the development of new transistors, that have higher on to off current ratios. The rare-earth nickelates were first made by Demazeau et al. in 1971, by heating a mixture of oxides under high pressure oxygen, or potassium perchlorate. However they were unable to make the cerium, praseodymium, and terbium nickelates. This may be because Ce, Pr and Tb oxidises to ⁴⁺ions in those conditions. For two decades after that no one paid attention to them. Many rare-earth nickelates have the Ruddlesden–Popper phase structure.

List of oxides

References

{{nickel compounds Nickel compounds Transition metal oxyanions Oxometallates

Alkali nickelates

Rare-earth nickelates

List of oxides

See also

References