Nickel(II) nitrite
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Nickel(II) nitrite is an inorganic compound with the
chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...
Ni(NO2)2. Anhydrous nickel nitrite was first discovered in 1961 by Cyril Clifford Addison, who allowed gaseous nickel tetracarbonyl to react with dinitrogen tetroxide, yielding a green smoke. Nickel nitrite was the second transition element anhydrous nitrite discovered after silver nitrite.


Properties

Nickel nitrite decomposes when heated to 220°C, however it can be heated up to 260°C in argon. The nitrite is covalently bonded to nickel, and the material is slightly volatile. The infrared spectrum of the solid has absorption bands at 1575, 1388, 1333, 1240, 1080, and 830 cm−1. Liquid dinitrogen tetroxide oxidises nickel nitrite to nickel nitrate.


In solution

When nickel nitrite dissolves in water, different mixed nitro-aqua complexes form such as Ni(NO2)2(H2O)4, , and . The aqueous complex Ni(NO2)2(H2O)4 forms when an alkali metal nitrite is added to a nickel salt solution: : + 2 Ni(NO2)2(H2O)4 + 2 H2O; ''K'' = 0.16 at standard conditions The complex is a much more intense emerald green colour than the Ni(H2O)62+ ion. Brooker claims that intense light photocatalyses the destruction of the ionic nitro complexes, leaving only Ni(NO2)2(H2O)4. Nickel nitrite slowly decomposes slightly in aqueous solution due to
disproportionation In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can ...
: :3 NO2− + 2 H+ → 2 NO(g) + NO3– + H2O


Complexes

In the presence of additional ligands, nickel nitrite can change colors substantially. These color changes may arise from the new molecular orbitals, or linkage isomerism, in which the nitro ligands rearrange to a nitrito (-ONO) complex. Sorted by color, known compounds include: * * * ; Violet :* Ni( (Me2N)Pyr)2(ONO)2 ; Reddish blue-violet :* Ni( (MeNH)Pyr)2(NO2)2 ; Blue-gray :* Ni( C(MeNH)H(CH2)3(CMeH)NH)2(ONO)2 ; Blue :* Ni( Pyr)4(ONO)2 :* Ni( N,N-Et2en)2(NO2)2 :* Ni( C(Me2N)H(CH2)4NH)2(ONO)2 :* Ni( (MeNH)(Me)Pyr)2(ONO)2 ; Blue-green :* Ni( R en)2(ONO)2 :* Ni( N,N'-Et2en)2(NO2)2 ; Green :* Ni( α-MePyr)2(NO2)2 :* Ni( C9H7N)2(NO2)2 ; Red :* Ni(NO2)2(NH3)4 :* Ni( en)2(NO2)2 :* Ni( R- en)2(NO2)2 :* Ni( (NH2CH2)(NH2)''i''Pr)2(NO2)2 :* Ni( Et-en)2(NO2)2 :* Ni( ''rac''- Ph2en)2(NO2)2 :* Ni( C(MeNH)H(CH2)4NH)2(NO2)2 :* Ni( N,N'-Me2en)2(NO2)2•H2O :* Ni( N,N-Me2en)2(NO2)2 ; Pink :* Ni( Me-en)2(NO2)2


Double salts

The nitronickelates are related compounds where more nitro groups are attached to nickel to yield an anion. They could be described as nickel double nitrites.


References

{{Nickel compounds Nickel compounds Nitrites Substances discovered in the 1960s