# 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.

• In this paper, it is reported that $\ce{Ni(SCN)2}$ is yellow: link.springer.com/article/10.1007%2FBF00935928 – Jannis Andreska Oct 7 '14 at 18:16
• @JannisAndreska Is it anhydrous? Most Ni(II) salts are yellow in anhydrous form and green in hydrate form. – t.c Oct 7 '14 at 18:19
• @t.c I think they are referring to the anhydrous salt. – Jannis Andreska Oct 7 '14 at 18:21

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.

Reference:ChemicalBook

Chemical Book 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).

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.

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.

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.

As @permeakra said, the color 'depends'. The color various in different forms. From atomistry.com:

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.