Tetrabromonickelate

The tetrabromonickelate anion contains a doubly-charged nickel atom (Ni2+) surrounded by four bromide ions in a tetrahedral arrangement. The formula is [NiBr4]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.[1] Solvents that can dissolve tetrabromonickelate include acetone, acetonitrile, methyl ethyl ketone, and nitromethane.[2]

In the visible absorption spectrum there is a strong absorption band termed ν3 near 710 nm which is caused by an electronic transition from 3T1(F) → 3T1(P). Another strong absorption in the near infrared called ν2 near 770 nm is due to the 3T1(F) → 3A2(F) transition.[2]

Salts

Dilithium tetrabromonickelate forms a dark blue solution in tetrahydrofuran.[3]

A mixture of lithium bromide and nickel bromide in water or methanol can transfer [NiBr4]2− ions into a cyclohexane-amine mixture. The solution formed is green.[4]

Tetraethylammonium tetrabromonickelate[5] is blue.[6]

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.[7]

Tetraphenylphosphonium tetrabromonickelate(II)[1] can be made from nickel bromide, triphenylphosphine, and bromobenzene 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.[8]

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.[9]

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.[10]

bis-(tetra-n-butylphosphonium) tetrabromonickelate can form as a glass when nickel bromide is dissolved in molten tetra-n-butylphosphonium iodide.[11]

Blue 1,1,1-trimethylhydrazinium tetrabromonickelate [H2NN(CH3)3]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.[12]

One bromine atom can be substituted by other ligands, such as triphenylphosphine, to make a dark green triphenylphosphinetribromonickelate ion.[8] Analogous tetrahedral nickelates include tetrafluoronickelates, tetrachloronickelates, tetraiodonickelates, and tetracyanonickelates.

References
  1. Goodgame, D. M. L.; Goodgame, M.; Cotton, F. A. (October 1961). "Electronic Spectra of Some Tetrahedral Nickel(II) Complexes". Journal of the American Chemical Society. 83 (20): 4161–4167. doi:10.1021/ja01481a014.
  2. Fine, Dwight A. (March 1965). "Tetrahedral Bromide Complexes of Nickel(II) in Organic Solvents". Inorganic Chemistry. 4 (3): 345–350. doi:10.1021/ic50025a019.
  3. Fertel, Lawrence B. (15 April 2001). Dilithium Tetrabromonickelate(II). E-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rd267. ISBN 978-0471936237.
  4. Florence, T. M.; Farrar, Yvonne J. (July 1968). "Liquid-liquid extraction of nickel with long-chain amines from aqueous and nonaqueous halide media". Analytical Chemistry. 40 (8): 1200–1206. doi:10.1021/ac60264a010.
  5. Inman, Guy W.; Hatfield, William E.; Jones, Edwin R. (August 1971). "The magnetic properties of tetraethylammonium tetrachloronickelate(II) and tetraethylammonium tetrabromonickelate(II)". Inorganic and Nuclear Chemistry Letters. 7 (8): 721–723. doi:10.1016/0020-1650(71)80078-8.
  6. Gill, Naida S.; Nyholm, R. S. (1959). "802. Complex halides of the transition metals. Part I. Tetrahedral nickel complexes". Journal of the Chemical Society (Resumed): 3997. doi:10.1039/JR9590003997.
  7. Smith, G. Pedro.; Liu, C. H.; Griffiths, Trevor R. (November 1964). "Charge-Transfer and Ligand-Field Spectra of Tetrahedral Tetrahalonickel(II) Ions in Molten Dimethyl Sulfone and Molten Organic Halide Salts". Journal of the American Chemical Society. 86 (22): 4796–4802. doi:10.1021/ja01076a014.
  8. Cotton, F. A.; Faut, O. D.; Goodgame, D. M. L. (January 1961). "Preparation, Spectra and Electronic Structures of Tetrahedral Nickel(II) Complexes Containing Triphenylphosphine and Halide Ions as Ligands". Journal of the American Chemical Society. 83 (2): 344–351. doi:10.1021/ja01463a021.
  9. Tsou, T. T.; Kochi, J. K. (December 1979). "Mechanism of biaryl synthesis with nickel complexes". Journal of the American Chemical Society. 101 (25): 7547–7560. doi:10.1021/ja00519a015.
  10. Previdi, John C.; Krause, Ronald A. (February 1976). "Ligand alkylation of bis(N,N-diethyldithiocarbamato) nickel(II) by α,α'-dibromo-o-xylene". Inorganic Chemistry. 15 (2): 462–464. doi:10.1021/ic50156a044.
  11. Islam, N.; Islam, M. R.; Ahmad, S.; Waris, B. (May 1975). "Optical spectra and the free-volume model for the transport behavior of glass-forming melts". Journal of the American Chemical Society. 97 (11): 3026–3032. doi:10.1021/ja00844a018.
  12. Goedken, V. L.; Vallarino, L. M.; Quagliano, J. V. (December 1971). "Cationic ligands. Coordination of the 1,1,1-trimethylhydrazinium cation to nickel(II)". Inorganic Chemistry. 10 (12): 2682–2685. doi:10.1021/ic50106a011.
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