The following ligand is
(a) hexadentate
(b) tetradentate
(c) bidentate
(d) tridentate

Q: What exactly is a ligand?

A ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. It acts as a Lewis base by donating electron pairs to the metal, which acts as a Lewis acid.

Q: How do I quickly identify a donor atom in a complex structure?

Donor atoms typically have at least one lone pair of electrons (like neutral N, O, S) or carry a negative formal charge (like Cl^-, O^-) that they can readily share with the electron-deficient metal ion.

Q: Why are the benzene rings themselves not considered donor sites here?

While benzene rings have a cloud of pi-electrons, they generally do not act as standard donor sites in classical coordination complexes unless they are forming specific organometallic pi-complexes. In this molecule, the localized lone pairs on the Nitrogen and the negatively charged Oxygen atoms are vastly stronger and more accessible donors.

Q: Does the physical size of the ligand affect its denticity?

Not directly. Denticity is strictly the *count* of donor atoms. However, larger multidentate ligands often form much more stable complexes due to the 'chelate effect', as they can wrap around the metal ion.

Q: What does the prefix 'tetra-' in tetradentate mean?

'Tetra' is the Greek prefix for four, and 'dentate' comes from the Latin word for tooth. So, a tetradentate ligand is one that 'bites' onto the metal ion at four different places using its four donor atoms.

Question

The following ligand is

Options:

(A) hexadentate

(B) tetradentate

(C) bidentate

(D) tridentate

Sigma Percentile · Accepted Answer

### Decoding the Ligand

When you first look at a large, complex organic molecule acting as a ligand, it can seem intimidating. However, the key to understanding its behavior in coordination chemistry lies in a very simple concept: **denticity**.

Denticity is essentially the number of "teeth" or "hands" a single ligand molecule possesses to grab onto a central metal ion. In chemical terms, it is the total number of **donor atoms** within the molecule that are capable of donating an electron pair to form a coordinate covalent bond.

### Hunting for Donor Atoms

To determine the denticity, we must act as molecular detectives and scan the structure for potential donor sites. We are specifically looking for atoms that are electron-rich—typically those with **lone pairs of electrons** (like neutral Nitrogen, Oxygen, or Sulfur) or those carrying a **negative formal charge**.

Let's break down the given ligand:

1.  **The Nitrogen Donors:** If we look at the upper portion of the molecule, we find two nitrogen atoms. One is a central tertiary amine acting as a structural hub, and the other is part of a diethylamine ($-NEt_2$) group. Both of these nitrogen atoms possess a localized lone pair of electrons. This gives us our first **two donor sites**.

2.  **The Oxygen Donors:** Moving to the lower section, we see two benzene rings. Attached to each ring is an oxygen atom carrying a negative charge ($-O^-$), forming phenoxide groups. These negatively charged oxygen atoms are highly nucleophilic and are exceptionally strong donor sites. This provides us with **two additional donor sites**.

### The Final Verdict

Now, we simply tally up our findings:

$$	ext{Total Donor Atoms} = 2 	ext{ (Nitrogen)} + 2 	ext{ (Oxygen)} = 4$$

Because this single ligand molecule can simultaneously form four coordinate bonds with a central metal ion, it is classified as a **tetradentate** ligand.

Ligands with high denticity, like this one, are incredibly important in chemistry because they wrap around the metal ion, forming multiple ring structures. This phenomenon, known as the **chelate effect**, leads to coordination complexes that are thermodynamically exceptionally stable.

Animated Solution for Chemistry - Coordination Compounds: The following ligand is

Select Answer:

Visualized Solution

$Visualizing the Ligand$

$Concept of Denticity$

$Identifying Nitrogen Donors$

$Identifying Oxygen Donors$

$Calculating Total Denticity$

$The Chelate Effect$

The Sigma Insight: Nomenclature, Isomerism, Importance and Werner's Theory

Decoding the Ligand

Hunting for Donor Atoms

The Final Verdict

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Animated Solution for Chemistry - Coordination Compounds: The following ligand is

Select Answer:

Visualized Solution

.math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } Visualizing the Ligand

.math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } Concept of Denticity

.math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } Identifying Nitrogen Donors

.math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } Identifying Oxygen Donors

.math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } Calculating Total Denticity

.math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } The Chelate Effect