The tetrabromonickelate anion contains a doubly-charged nickel atom (Ni²⁺) surrounded by four

bromide A bromide ion is the negatively charged form (Br−) of the element bromine, a member of the halogens group on the periodic table. Most bromides are colorless. Bromides have many practical roles, being found in anticonvulsants, flame-retardant ...

ions in a

tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...

arrangement. The formula is iBr₄sup>2−. The anion combines with cations to form a series of salts called tetrabromonickelates. Strongly-coordinating solvents will displace one or more of the bromido ligands from the complex. Solvents that can dissolve tetrabromonickelate include

acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscib ...

, acetonitrile, methyl ethyl ketone, and

nitromethane Nitromethane, sometimes shortened to simply "nitro", is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a polar liquid commonly used as a solvent in a variety of industrial applications such as in ...

. In the visible absorption spectrum there is a strong absorption band termed ''ν''₃ near 710 nm which is caused by an

electronic transition A quantum jump is the abrupt transition of a quantum system (atom, molecule, atomic nucleus) from one quantum state to another, from one energy level to another. When the system absorbs energy, there is a transition to a higher energy level (ex ...

from ³T₁(F) → ³T₁(P). Another strong absorption in the

near infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from arou ...

called ''ν''₂ near 770 nm is due to the ³T₁(F) → ³A₂(F) transition.

Salts

Dilithium tetrabromonickelate forms a dark blue solution in

tetrahydrofuran Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...

. A mixture of lithium bromide and nickel bromide in water or methanol can transfer iBr₄sup>2− ions into a cyclohexane-amine mixture. The solution formed is green. Tetraethylammonium tetrabromonickelate is blue. tetra-''n''-butylammonium tetrabromonickelate is purple blue in color, melting around 83°C. It is formed from nickel bromide and tetra-''n''-butylammonium bromide in

ethyl alcohol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a hyd ...

. Tetraphenylphosphonium tetrabromonickelate(II) can be made from nickel bromide,

triphenylphosphine Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists ...

, and

bromobenzene Bromobenzene is an aryl halide, C6H5Br. It is a colourless liquid although older samples can appear yellow. It is a reagent in organic synthesis. Synthesis and reactions Bromobenzene is prepared by the action of bromine on benzene in the presenc ...

by heating them together in a sealed tube at 250 °C. This substance is dark blue. If it is heated over 260° the color changes to green, and it melts at 273 °C. A dark blue oil, bis-(''o''-tolyltriethylphosphonium) tetrabromonickelate (o-CH₃C₆H₆PEt₃)₂NiBr₄ can be made from the reaction of ''o''-tolyl bis-triethylphosphine, nickel bromide and ''o''-tolyl bromide. (o-CH₃OC₆H₆PEt₃)₂NiBr₄ and (C₆H₅PEt₃)₂NiBr₄ are made in a similar way. bis-(benzo 'e''1,3-dithiepan-2-diethylimmonium) tetrabromonickelate, abbreviated as (xdtc)₂NiBr₄, has dark blue crystals that melt at 166 °C. It is made from α,α'-dibromo-''o''-xylene and bis-(''N,N''-diethyldithiocarbamato)nickel(II) dissolved in 1,2-dichloroethane. bis-(tetra-''n''-butylphosphonium) tetrabromonickelate can form as a glass when nickel bromide is dissolved in molten tetra-''n''-butylphosphonium iodide. Blue 1,1,1-trimethylhydrazinium tetrabromonickelate ₂NN(CH₃)₃sub>2NiBr₄ is a salt stable between 70° and 260 °C. It can be formed by heating an octahedral neutral nickel complex where the trimethylhydrazinium and bromide are all ligands on a nickel atom. The salt decomposes at room temperature to polymeric trimethylhydrazinium nickel tribromide. The salt decomposes when dissolved in polar solvents, due to

solvolysis In chemistry, solvolysis is a type of nucleophilic substitution (S1/S2) or elimination reaction, elimination where the nucleophile is a solvent molecule. Characteristic of S1 reactions, solvolysis of a chirality (chemistry), chiral reactant affor ...

One bromine atom can be substituted by other ligands, such as

, to make a dark green triphenylphosphinetribromonickelate ion. Analogous tetrahedral nickelates include

tetrafluoronickelate The fluoronickelates are a class of chemical compounds containing an anion with nickel at its core, surrounded by fluoride ions which act as ligands. This makes it a fluoroanion In chemistry, a fluoroanion or fluorometallate anion is a polyatomi ...

s, tetrachloronickelates, tetraiodonickelates, and tetracyanonickelates.

References

{{nickel compounds Nickel complexes Bromometallates

Salts

Related

References