Question

Identify the correct formula for $\text{potassium tetracyanonickelate(II)}$.

• A. $K\left[Ni\right(CN{)}_4]$
• B. $K\left[Ni\right(CN{)}_4{]}_2$
• C. $K_2\left[Ni\right(CN{)}_4]$
• D. $Ni\left[K\right(CN{)}_4]$

Answer 1

The correct option is C $K_2\left[Ni\right(CN{)}_4]$

The parenthesis after nickelate in IUPAC name represents its oxidation state (+2).
Thus, the central metal atom is nickel and its oxidation state is +2.

Cyano- Negative ligand $\left(C{N}^{-}\right)$
Tetracyano- 4$C{N}^{-}$ ligand.

So, the charge on coordination entity will be $-4+2=-2$.
This -2 charge must be balanced by potassium ions which have charge of +1.
Hence the formula of given coordination compound is $K_2\left[Ni\right(CN{)}_4].$