Animated Solution for Chemistry - Coordination Compounds: In the coordination compound, $K_4[Ni(CN{)}_4]$ the oxidation state of nickel is

Finding the oxidation state of a central metal atom in a coordination compound is a fundamental skill in chemistry. It's like solving a tiny algebraic puzzle where the pieces are the charges of the individual components.

Let's look at our given complex: $K_4[Ni(CN{)}_4]$.

This compound consists of two main parts: the counter ions outside the square brackets and the complex ion inside the square brackets. The first step to finding the oxidation state of the central metal, Nickel ($Ni$), is to determine the net charge on the complex ion itself.

Imagine dissolving this compound in water. The counter ions will separate from the coordination sphere.

Potassium ($K$) is an alkali metal, meaning it always carries a $+1$ charge in its ionic form. Since there are four potassium ions, they contribute a total charge of $+4$. For the entire compound to be electrically neutral, the complex ion $[Ni(CN{)}_4]$ must carry an equal and opposite charge. Therefore, the net charge on the complex ion is $-4$.

Now, we focus entirely on the complex ion: $[Ni(CN{)}_4{]}^{4-}$.

The net charge of a complex ion is simply the sum of the oxidation state of the central metal and the total charge of all the ligands attached to it.

Let the oxidation state of Nickel be $x$.

We know that the cyanide ligand ($C{N}^{-}$) is a well-known anion with a charge of $-1$. Since there are four cyanide ligands, their total charge contribution is $4\times (-1)=-4$.

Setting up our algebraic equation:

Now, it's just a matter of simple arithmetic.

Moving the $-4$ to the other side of the equation:

We have found that the oxidation state of Nickel in this complex is $0$.

While it might seem unusual for a metal to have a zero oxidation state, it is actually quite common in coordination chemistry, especially when the metal is bonded to strong $\pi$-acceptor ligands like cyanide ($C{N}^{-}$) or carbon monoxide ($CO$). These ligands have empty anti-bonding orbitals that can accept electron density back from the metal, a process known as synergic bonding or $\pi$-backbonding, which beautifully stabilizes the zero oxidation state.