Chemistry - Coordination Chemistry Question with Solution | TestHub

Copper Reaction: $C{u}^{2+}$ reacts with excess $KCN$ to first form unstable $Cu(CN{)}_2$, which decomposes into stable $CuCN$ and liberates cyanogen gas $(CN{)}_2$.

Gas Structure: The structure of cyanogen gas is $N\equiv C-C\equiv N$, which contains exactly 3 $\sigma$-bonds (one $C-C$ and two $C-N$) and 4 $\pi$-bonds.

Complex Formation: $CuCN$ further dissolves in excess $C{N}^{-}$ to form the stable, diamagnetic complex $[Cu(CN{)}_4{]}^{3-}$.

Cadmium Reaction: $C{d}^{2+}$ directly forms the stable complex $[Cd(CN{)}_4{]}^{2-}$ with no gas evolution.