I did a little investigation of what happens when thiocyanate (as KSCN) is added to a copper (II) solution (as CuSO4).
(This was sort of inspired by a question about an unknown copper compound posted on this board as well as sci.chem.)
The results were more complicated than I expected. Upon adding small amounts of SCN- ion (less than 1.0 molar ratio compared to Cu(II)), I saw an apple-green solution, with a small amount of pinkish-gray precipitate. Upon adding more SCN-, up to 1.6 molar ratio or so, more precipitate formed, and the green color of the solution gradually faded. As even more SCN- was added, up to around 2.2 molar ratio, the solution changed to pale yellow, no longer green at all.
I suspect that the pinkish precipitate is Cu(I)SCN, formed as SCN- reduced Cu(II) to Cu(I), becoming oxidised to (SCN)2. (Thanks to Borek for this suggestion). My CRC describes Cu(I)SCN as white, (nearly) insoluble in H2O, insoluble in alcohol, and soluble in NH3(aq). My precipitate did not dissolve in EtOH, and did dissolve in 2.5 m NH3, forming a deep blue solution that looks like copper tetraamine. This is consistent with the CRC properties of Cu(I)SCN.
The CRC describes Cu(II)(SCN)2 as a black solid, which decomposes in H2O (to what?), and also describes (SCN)2 as yellow (liquid at room temp) which also decomposes in H2O (to what?).
I wonder what my green and yellow solutions are. The green might be some complex of Cu(II) and SCN-, or it might be the decomposition products of Cu(II)(SCN)2 with water. The yellow might be the decomposition products of (SCN)2. I don't know, however, and ask if aybody here has any insight.
I am attaching a photo of the products, L to R these are the green solution (low SCN amount), pink precipitate (Cu(I)SCN), and yellow solution (large SCN amount).