Wikipedia
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)] 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 D. The distance from the nickel atom to the carbon is 1.87 Å, and the carbon-nitrogen distance is 1.16 Å. Tetracyanonickelate(II) can be oxidised electrochemically in solution to yield tetracyanonickelate(III) [Ni(CN)]. [Ni(CN)] is unstable and Ni(III) oxidises the cyanide to cyanate OCN. Tetracyanonickelate(III) can add two more cyanide groups to form hexacyanonickelate(III).
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.
If the cation is a very strong reducing agent, such as Yb, [Ni(CN)] can be reduced to [Ni(CN)] where nickel atom is in the +1 oxidation state.
formula
name
Ni Ox
structure
Remarks
references
Na[Ni(CN)].3HO
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 Å FW=262.81
orange; Ni(CN) planes parallel
K[Ni(CN)]•HO
potassium tetracyanonickelate(II)
2
monoclinic
orange-red; dehydrate at 110°
K[Ni(CN)]
potassium tetracyanonickelate(II)
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
Ca[Ni(CN)]•5HO
calcium tetracyanonickelate(II)
2
orthorhombic Pcab a=18.18 Å, b=18.86 Å, c=6.774 Å, Z=8, V=2195 Å, density=1.774
CN forms distorted square around Ni; yellow when light polarized in elongation direction, colourless ⊥
Co•2HO[Ni(CN)]•4HO
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
Ni(NH)[Ni(CN)]•CH
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.
Rb[Ni(CN)]•HO
rubidium tetracyanonickelate(II)
2
triclinic P a=8.602 Å, b=9.693 Å, c=12.006 Å, α = 92.621°, β= 94.263∘, γ =111.79° V=924.0 Å
orange needles; Ni(CN) planes parallel; water in 5% excess
Sr[Ni(CN)]•5HO
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 Å
orange; Ni(CN) planes parallel
Cd•2HO[Ni(CN)]•4HO
diaquacadmium tetracyanonickelate tetrahydrate
2
orthorhombic Pnma, a = 12.393 Å, b = 14.278 Å, c = 7.427 Å, Z = 4, V=1314 Å, density=1.937
MW=383.27
Cs[Ni(CN)]•1.05HO
Cesium tetracyanonickelate(II)
2
hexagonal, P61, a = 9.526 Å, c = 19.043 Å, V = 1496.5 Å Z=6
golden yellow; Ni(CN) planes arranged in a spiral
CsKNi(CN)
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
Ba[Ni(CN)]•4HO
barium tetracyanonickelate(II)
2
monoclinic
red
(dmf)EuNi(CN)
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
Tl[Ni(CN)]•1.05HO
Thallium 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
(UO)[Ni(CN)]
2
monoclinic C2/c a=21.522 Å, b=10.2531 Å, c=13.3170 Å, β=111.943° V=2725.8 Å
yellow
K[(CN)Ni(CN)Ni(CN)]
potassium tetracyano-µ-dicyanonickelate(I)
1