Colour of Nickel thiocyanate

What is the colour of $\ce{C2N2NiS2}$ (Nickel thiocyanate)? 


In most of the web sites it only molecular weight,formula and other specifications but its colour is missing every where.




[Chemical Book](https://www.chemicalbook.com/ChemicalProductProperty_EN_CB2725417.htm) describes nickel(II) thiocyanate (CAS #: 13689-92-4) as "Nickel Thiocyanate Greenpowder" (see Freddy's answer elsewhere), but according to the Ref.1, it is **yellow** in color:



> 
> [...] This chloroform solution was green in contrast to the usual intense blue of nickel amino complexes. When the chloroform was allowed to evaporate, a viscous green scum was left. There was no evidence of crystallinity. This green amorphous matter was allowed to stand in the air for a few days and in that time the product had largely decomposed to **yellow nickel thiocyanate**.
> 
> 
> 


This work has been published in a peer-review journal (Ref.2) so that I tends to believe this report, which is also supported by Matt Cliffe's and permeakra's answers.


**References:**


1. Don Wayne Carle, "The preparation of nickel(II) thiocyanate complex compounds with certain organic bases and the determination of their heats of formation," *MS Thesis* **1952**, Oregon State College, OR, USA.
2. Albert V. Logan, Don W. Carle, "The Preparation of Nickel(II) Thiocyanate Complex Compounds with Picolines and the Determination of their Heats of Formation," *J. Am. Chem. Soc.* **1952**, *74(20)*, 5224–5225 (<https://doi.org/10.1021/ja01140a517>).


 4

After bit research i got finally one link where they mentioned the colour. The other name of(Synonym) of Nickel thiocyanate is "Nickel Thiocyanate Greenpowder" which suggest it is **Green** in colour. 




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Reference:[ChemicalBook](http://www.chemicalbook.com/ChemicalProductProperty_EN_CB2725417.htm) 


 2

It's a kind of a yellow/green brown, assuming you mean the solid. Aqueous (and similar solvents) solutions are green.


**Reference**


1. Dubler, E., Relier, A., & Oswald, H. R. (**1982**). Intermediates in
thermal decomposition of nickel (II) complexes: The crystal
structures of Ni(SCN)2(NH3)2 and Ni(SCN)2, Zeitschrift für
Kristallographie-Crystalline Materials, 161(1-4), 265-278.


 2

The proper answer 'it depends'



> 
> PROPERTIES:
>  Formula weight 174.88. Dark chocolate-colored powder. On
>  addition of water, becomes first yellow and then dissolves with a
>  green color.
> 
> 
> 


(c) Brauer


In general you should be extremely cautious guessing colors of $d$-metal salts when the metal ion is not hydrated. The color may range widely. The only reasonably safe assumption is that $d^0$-salts are usually colorless, but then agains $\ce{MnO4-}$ is violet, so the colors must be memorized separately for each case.


 1

As @permeakra said, the color 'depends'. The color various in different forms. From [atomistry.com](http://nickel.atomistry.com/nickel_thiocyanate.html):



> 
> Nickel Thiocyanate, $\ce{Ni(CNS)2}$, has been obtained in the
> anhydrous condition as a **chocolate-coloured amorphous powder**. The
> hydrated salt, $\ce{2Ni(SCN)2.3H2O}$, obtained by dissolving nickel
> carbonate in thiocyanic acid is a **yellowish brown crystalline powder**.
> 
> 
> 


 1

Most hydrated Ni(II) salts are green.


For transition metals, its salts are often colored because of transitions of electrons between d-orbitals of different energy, and such transitions release protons of a specific wavelength (which happen to be within the visible range of light for most d block elements).


Therefore, for a transition metal with the same oxidation state, its hydrated salts often exhibit a characteristic color.
In fact for most transition metal salts, the color can be predicted simply by knowing the cation of the salt.


<http://en.wikipedia.org/wiki/Color_of_chemicals#Ions_in_aqueous_solution>


For example, Cu(II) salts are blue, Ni(II) salts are green. 


As thiocyanate has the charge of -1, the nickel in $\ce{Ni(SCN)2}$ has the charge of +2, and $\ce{Ni(SCN)2}$ is therefore green, as confirmed in the answer given by @hey. 


 0