Number of ambidentate ligands in a representative metal complex [M(en)(SCN)₄] is ___________.
[en = ethylenediamine]

Solution

Chemistry ma’am · 4 steps

Ambidentate means two possible donor atoms but only one used at a time, so count only the SCN ligands here.

1. What ambidentate means. An ambidentate ligand has two different atoms that can donate, but it binds through only one of them at a time. Thiocyanate can bind through S as SCN⁻ or through N as NCS⁻.
2. Check en. Ethylenediamine, H₂N-CH₂-CH₂-NH₂, binds through both N atoms at the same time. That makes it bidentate (a chelating ligand), not ambidentate.
3. Count the SCN. The complex has four SCN⁻ ligands. Each one is ambidentate on its own, so each one counts.
4. So. The complex has 4 ambidentate ligands, giving 4.

The common slip: 5. Counting en as ambidentate because it has two N donors gives 5. Both its N atoms bind together, so it is bidentate.

The idea to keep. Ambidentate means two donor sites with only one used at a time (SCN⁻, NO₂⁻, CN⁻). A ligand that uses both donors at once, like en, is bidentate.

Answer from the NTA final answer key. Solution by PrepWiser.