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A tetrahedral tetrachloronickelate complex ion

Tetrachloronickelate is the metal complex with the formula [NiCl₄]²⁻. Salts of the complex are available with a variety of cations, but a common one is tetraethylammonium.^[1]

When concentrated lithium chloride and nickel chloride solution in water is mixed, only a pentaaquachloro complex is formed: [Ni(H₂O)₅Cl]⁺. However in other organic solvents, or molten salts the tetrachloronickelate ion can form. Nickel can be separated from such a solution in water or methanol, by partitioning it into a cyclohexane solution of amines.^[2]

Organic ammonium salts of the type (R₃NH)₂[NiCl₄] are often thermochromic (R = Me, Et, Pr). Near room temperature, these salts are yellow , but these solids become blue when heated to near 70 °C. The bright blue color is characteristic of tetrahedral [NiCl₄]²⁻, the intensity being a consequence of the Laporte selection rule. The yellow color results from a polymer consisting of octahedral Ni centers. The corresponding tetrabromonickelates are also thermochromic with a lower transition temperatures.^[3]

History

The blue colour due to the tetrachloronickelate ion was first observed in 1944 when Remy and Meyer melted caesium chloride and caesium nickel trichloride together.^[4]

Compounds

formula	name	structure	Remarks	references
Cs₂NiCl₄	caesium tetrachloronickelate		blue, stable only over 70°	^[4]
[(CH₃)₄N]₂NiCl₄	Tetramethylammonium tetrachloronickelate		dark blue	^[5]
[(C₂H₅)₄N]₂NiCl₄	Tetraethylammonium tetrachloronickelate			^[6]^[4]
[H₂NN(CH₃)₃]₂NiCl₄	1,1,1-trimethylhydrazinium tetrachloronickelate		blue, only stable over 145 °C, under this is yellow	^[7]
[(C₆H₅)₄As]₂NiCl₄	bis-tetraphenylarsonium tetrachloronickelate		blue, melts at 199.5°C	^[5]
[(C₆H₅)₃CH₃As]₂NiCl₄	bis-triphenylmethylarsonium tetrachloronickelate		blue	^[4]
[C₂mim]₂NiCl₄	1-ethyl-3-methylimidazolium tetrachloronickelate(II)	tetragonal I4₁/a a=14.112 c=19.436 V=3871.1 Z=8 density=1.47 MW=422.84	melts at 92°	^[8]^[9]
[C₄mim]₂NiCl₄	1-butyl-3-methylimidazolium tetrachloronickelate(II)	dark blue, melts at 56°C		^[8]
[C₅mim]₂NiCl₄	1-pentyl-3-methylimidazolium tetrachloronickelate(II)	dark blue liquid		^[8]
[C₆mim]₂NiCl₄	1-hexyl-3-methylimidazolium tetrachloronickelate(II)	dark blue liquid		^[8]
[C₇mim]₂NiCl₄	1-heptyl-3-methylimidazolium tetrachloronickelate(II)	dark blue liquid		^[8]
[C₈mim]₂NiCl₄	1-octyl-3-methylimidazolium tetrachloronickelate(II)	dark blue liquid		^[8]
[NH₃CH₂CH₂NH₃]NiCl₄	ethylenediammonium tetrachloronickelate(II)	perovskite layered, space group P2₁/c a=8.441, b=6.995, c=6.943, β=92.925 Z=2	brown, isostructural with Mn, Cu, Pd, and Cd compounds	^[10]

Related substances

tetrabromonickelates

References

^ Naida S. Gill; F. B. Taylor (1967). "Tetrahalo Complexes of Dipositive Metals in the First Transition Series". Inorganic Syntheses. Vol. 9. pp. 136–142. doi:10.1002/9780470132401.ch37. ISBN 978-0-470-13240-1.
^ 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.
^ Ferraro, John R.; Sheren, Anne T. (3 February 1978). "Some new thermochromic complexes of Nickel(II) of the type [R/sub x/NH/sub 4-x/]2NiCl4". Inorganic Chemistry. 17 (9): 2498–2502. doi:10.1021/ic50187a032.
^ ^a ^b ^c ^d 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.
^ ^a ^b 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.
^ 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.
^ 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.
^ ^a ^b ^c ^d ^e ^f Meredith, M. Brett; McMillen, C. Heather; Goodman, Jonathan T.; Hanusa, Timothy P. (August 2009). "Ambient temperature imidazolium-based ionic liquids with tetrachloronickelate(II) anions". Polyhedron. 28 (12): 2355–2358. doi:10.1016/j.poly.2009.04.037.
^ Hitchcock, Peter B.; Seddon, Kenneth R.; Welton, Thomas (1993). "Hydrogen-bond acceptor abilities of tetrachlorometalate(II) complexes in ionic liquids". Journal of the Chemical Society, Dalton Transactions (17): 2639. doi:10.1039/DT9930002639.
^ Skaarup, Steen; Berg, Rolf Willestofte (September 1978). "Structural properties and vibrational spectra of the ethylene-diammonium family of perovskite layer-type crystals: [NH3CH2CH2NH3] [MCl4], M = Ni, Pd, Cu, Cd, Mn". Journal of Solid State Chemistry. 26 (1): 59–67. Bibcode:1978JSSCh..26...59S. doi:10.1016/0022-4596(78)90133-0.