The cyanonickelates are a class of chemical compound containing anions consisting of nickel atoms, and cyanide groups. The most important of these are the tetracyanonickelates containing four cyanide groups per nickel. The tetracyanonickelates contain the [Ni(CN)4]2− anion. This can exist in solution or in solid salts. The ion has cyanide groups arranged in a square around the central nickel ion. The symmetry of the ion is D4h. The distance from the nickel atom to the carbon is 1.87 Å, and the carbon-nitrogen distance is 1.16 Å.[1] Tetracyanonickelate(II) can be oxidised electrochemically in solution to yield tetracyanonickelate(III) [Ni(CN)4]. [Ni(CN)4] is unstable and Ni(III) oxidises the cyanide to cyanate OCN.[2] Tetracyanonickelate(III) can add two more cyanide groups to form hexacyanonickelate(III).[2]

Four cyano groups are arranged in a square in the tetracyanonickelate ion.
Potassium tetracyanonickelate(II) solution.
Potassium tetracyanonickelate(II) solid.

In combination with alkyldiamines, and other metal ions, tetracyanonickelate ions can form cage structure that can accommodate organic molecules. This is a Hofmann-diam-type clathrate.[3]

If the cation is a very strong reducing agent, such as Yb2+, [Ni(CN)4]2− can be reduced to [Ni2(CN)6]4− where nickel atom is in the +1 oxidation state.[4]

formula name Ni Ox structure Remarks references
Na2[Ni(CN)4]·3H2O disodium tetracyanonickelate(II) 2 triclinic a = 7.392 Å, b = 8.895 Å, c = 15.11 Å , α = 89.12, β= 87.46, γ = 84.54° Z=4 V=988 Å3 FW=262.81 orange; Ni(CN)4 planes parallel [5][6]
K2[Ni(CN)4]·H2O potassium tetracyanonickelate(II) 2 monoclinic orange-red; dehydrate at 110° [7]
K2[Ni(CN)4] Potassium tetracyanonickelate 2 monoclinic a=4.294 Å, b=7.680 Å, c=13.02 Å, β=87°16′ orange-yellow; CN forms a square around Ni [7]
Ca[Ni(CN)4]·5H2O calcium tetracyanonickelate(II) 2 orthorhombic Pcab a=18.18 Å, b=18.86 Å, c=6.774 Å, Z=8, V=2195 Å3, density=1.774 CN forms distorted square around Ni; yellow when light polarized in elongation direction, colourless ⊥ [8]
Co·2H2O[Ni(CN)4]·4H2O diaquacobalt tetracyanonickelate tetrahydrate 2 orthorhombic a=12.178 Å, b=13.885 Å, c=7.143 Å, V=1207.8 Z=4 orange MW=329.82 [9]
Ni(NH3)2[Ni(CN)4]·C6H6 Hofmann clathrate 2/2 benzene can be replaced by some other aromatic hydrocarbons; octahedral nickel can be replaced by Mn, Fe, Co, Cu, Zn or Cd. The square planar nickel can be replaced by Pd or Pt. Ammonia can be replaced by diamines and amines. [10]
Rb2[Ni(CN)4]·H2O rubidium tetracyanonickelate(II) 2 triclinic P1 a=8.602 Å, b=9.693 Å, c=12.006 Å, α = 92.621°, β= 94.263∘, γ =111.79° V=924.0 Å3 orange needles; Ni(CN)4 planes parallel; water in 5% excess [6]
Sr[Ni(CN)4]·5H2O strontium tetracyanonickelate(II) 2 monoclinic C2/m, a=10.356 Å, b=15.272 Å, c=7.133 Å, α=98.55°, V=1115.6 Å3 orange; Ni(CN)4 planes parallel [6]
Cd·2H2O[Ni(CN)4]·4H2O diaquacadmium tetracyanonickelate tetrahydrate 2 orthorhombic Pnma, a = 12.393 Å, b = 14.278 Å, c = 7.427 Å, Z = 4, V=1314 Å3, density=1.937 MW=383.27 [10]
Cs2[Ni(CN)4]·1.05H2O cesium tetracyanonickelate(II) 2 hexagonal, P61, a = 9.526 Å, c = 19.043 Å, V = 1496.5 Å3 Z=6 golden yellow; Ni(CN)4 planes arranged in a spiral [11]
CsKNi(CN)4 cesium potassium tetracyanonickelate 2 triclinic a= 7.421 Å, b= 8.626 Å, c= 9.364 Å, α= 60.64°,β= 70.88°, y= 70.88°, and Z= 2. den=2.55 orange [12]
Ba[Ni(CN)4]·4H2O barium tetracyanonickelate(II) 2 monoclinic red [13]
(dmf)4EuNi(CN)4 europium(II) tetracyanonickelate 2 triclinic P1̄, a=8.902Å, b=10.947Å, c = 12.464Å, α = 82.99°, β = 86.86°, γ = 84.92°, Z = 2 [4]
Tl2[Ni(CN)4]·1.05H2O thallium(I) tetracyanonickelate 2 monoclinic a=6.154 b=7.282 c=9.396 β=104.29 V=408.0 Z=2 density=4.652 bright yellow orange; chains of TlNi [12]
(UO2)2(dmso)4(OH)2[Ni(CN)4] 2 monoclinic C2/c a=21.522 Å, b=10.2531 Å, c=13.3170 Å, β=111.943° V=2725.8 Å yellow [14]
K4[(CN)3Ni-Ni(CN)3] potassium hexacyanodickelate(I) 1 "Bellucci's salt"[15]


  1. ^ Loewenschuss, A.; Marcus, Y. (1996). "Standard Thermodynamic Functions of Some Isolated Ions at 100–1000 К" (PDF). J. Phys. Chem. Ref. Data. 25 (6): 1502. Bibcode:1996JPCRD..25.1495L. doi:10.1063/1.555990. Retrieved 30 April 2016.
  2. ^ a b Wang, Yi Lai; Beach, Mark W.; Pappenhagen, Thomas L.; Margerum, Dale W. (November 1988). "Mixed-ligand complexes of tetracyanonickelate(III) and dynamic Jahn-Teller distortions of hexacyanonickelate(III)". Inorganic Chemistry. 27 (24): 4464–4472. doi:10.1021/ic00297a025.
  3. ^ Şenyel, Mustafa; Raci Sertbakan, T.; Kürkçüoğ, Güneş; Kasap, Ergün; Kantarci, Ziya (2001). "An Infrared Spectroscopic Study on the Hofmann-diam-type 1,12-Diaminododecanemetal(II) Tetracyanonickelate(II)-aromatic Guest Clathrates: M(H2N(CH2)12NH2)Ni(CN)4·G (M = Co, Ni or Cd; G = Benzene, Naphthalene, Anthracene, Phenanthrene or Biphenyl)". Journal of Inclusion Phenomena and Macrocyclic Chemistry. 39 (1/2): 175–180. doi:10.1023/A:1008141726024. S2CID 91455271.
  4. ^ a b Knoeppel, David W.; Shore, Sheldon G. (January 1996). "Unusual One-Dimensional Ladder Structures Containing Divalent Europium and the Tetracyanometalates Ni(CN)4 and Pt(CN)4". Inorganic Chemistry. 35 (18): 5328–5334. doi:10.1021/ic960337v.
  5. ^ Ptasiewicz-Bak, H.; Olovsson, I.; McIntyre, G. J. (1 October 1998). "Structure, Charge and Spin Density in Na2Ni(CN)4·3H2O at 295 and 30 K". Acta Crystallographica Section B. 54 (5): 600–612. doi:10.1107/S0108768198002286.
  6. ^ a b c Fronczek, Frank R.; Delord, Terry J.; Watkins, Steven F.; Gueorguieva, Petia; Stanley, George G.; Zizza, Annegret S.; Cornelius, Jeffrey B.; Mantz, Yves A.; Musselman, Ronald L. (November 2003). "A Solid-State Spectral Effect in Eclipsed Tetracyanonickelates: X-ray Crystal Structure, Polarized Specular Reflectance Spectroscopy, and ZINDO Modeling of Sr[Ni(CN)4]·5H2O, Rb2[Ni(CN)4]·H2O, and Na2[Ni(CN)4]·3H2O". Inorganic Chemistry. 42 (22): 7026–7036. doi:10.1021/ic0345222. PMID 14577768.
  7. ^ a b Vannerberg, Nils Gosta (1964). "The Crystal Structure of K2Ni(CN)4" (PDF). Acta Chemica Scandinavica. 18 (10): 2385–2391. doi:10.3891/acta.chem.scand.18-2385. Retrieved 29 April 2016. ICSD number 24099.
  8. ^ Holt, E. M.; Watson, K. J. (1969). "The Crystal Structure of Calcium Tetracyanonickelate (II)" (PDF). Acta Chemica Scandinavica. 23 (1): 14–28. doi:10.3891/acta.chem.scand.23-0014. Retrieved 29 April 2016.
  9. ^ Niu, T.; Crisci, G.; Lu, J.; Jacobson, A. J. (15 May 1998). "Diaquacobalt Tetracyanonickelate Tetrahydrate". Acta Crystallographica Section C. 54 (5): 565–567. doi:10.1107/S0108270197018003.
  10. ^ a b Ham, William K.; Weakley, Timothy J.R.; Page, Catherine J. (November 1993). "Synthesis and Crystal Structure of Cd(H2O)2Ni(CN)4·4H2O". Journal of Solid State Chemistry. 107 (1): 101–107. Bibcode:1993JSSCh.107..101H. doi:10.1006/jssc.1993.1327.
  11. ^ Cornelius, Jeffrey B.; Trapp, Robert M.; Delord, Terry J.; Fronczek, Frank R.; Watkins, Steven F.; Orosz, Jill Jasin; Musselman, Ronald L. (May 2003). "One-Dimensional Collective Electronic Effects in the Helically Stacked Cs2[Ni(CN)4]·H2O and Cs2[Pt(CN)4]·H2O: X-ray Structure, Polarized Specular Reflectance, and ZINDO Calculations". Inorganic Chemistry. 42 (9): 3026–3035. doi:10.1021/ic026101a. PMID 12716197.
  12. ^ a b Maliarik, Mikhail; Nagle, Jeffrey K.; Ilyukhin, Andrey; Murashova, Elena; Mink, János; Skripkin, Mikhail; Glaser, Julius; Kovacs, Margit; Horváth, Attila (May 2007). "Metal−Metal Bonding in Tetracyanometalates (M = Pt , Pd , Ni ) of Monovalent Thallium. Crystallographic and Spectroscopic Characterization of the New Compounds Tl2Ni(CN)4 and Tl2Pd(CN)4". Inorganic Chemistry. 46 (11): 4642–4653. doi:10.1021/ic062092k. PMID 17474737.
  13. ^ McCullough, R.L.; Jones, L.H.; Crosby, G.A. (January 1960). "An analysis of the vibrational spectrum of the tetracyanonickelate(II) ion in a crystal lattice". Spectrochimica Acta. 16 (8): 929–944. Bibcode:1960AcSpe..16..929M. doi:10.1016/0371-1951(60)80057-4.
  14. ^ Maynard, Branson A.; Lynn, K. Sabrina; Sykora, Richard E.; Gorden, Anne E. V. (6 May 2013). "Emission, Raman Spectroscopy, and Structural Characterization of Actinide Tetracyanometallates". Inorganic Chemistry. 52 (9): 4880–4889. doi:10.1021/ic302459z. ISSN 0020-1669. PMID 23594182.
  15. ^ Jarchow, O.; Schulz, H.; Nast, R. (1970). "Structure of the Anion in Solid K4[Ni2(CN)6]". Angewandte Chemie International Edition in English. 9: 71. doi:10.1002/anie.197000711.