Step 1: Understanding the Question:
An anionic ligand is a negatively charged ion that acts as a Lewis base to coordinate with a central metal atom.
Step 2: Detailed Explanation:
1. Tetraamminecopper (II) ion $[Cu(NH_3)_4]^{2+}$: The ligand is Ammine ($NH_3$), which is a neutral molecule.
2. Pentaammineaquacobalt (III) iodide $[Co(NH_3)_5(H_2O)]I_3$: The ligands are Ammine and Aqua, both are neutral. Iodide ($I^-$) is a counter ion, not a ligand in this name.
3. Tetracyanonickelate (II) ion $[Ni(CN)_4]^{2-}$: The ligand is Cyano ($CN^-$), which is a negatively charged (anionic) ligand.
4. Pentacarbonyliron(0) $[Fe(CO)_5]$: The ligand is Carbonyl ($CO$), which is neutral.
Step 4: Final Answer:
The complex $[Ni(CN)_4]^{2-}$ contains the anionic ligand $CN^-$.