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Consider the two complexation equilibria...

Consider the two complexation equilibria in aqueous solution, between the cobalt (II) ion `Co^(2+)` (aq) and ethylenediamine (en) on the one hand and ammonia `NH_(3)` on the other.
`[Co(H_(2)O)_(6)]^(2+)+6NH_(3)hArr[Co(NH_(3))_(6)]^(2+)+6H_(2)O` ...(1)
`[Co(H_(2)O_(6))]^(2+)+3enhArr[Co(en)_(3)]^(2+)+6H_(2)O` ..(2)
Electronicaly, the ammonia and en ligands are very similar, since both bond through N and since the liwis base strengths of their nitrogen atoms are similar. This means that `DeltaH^(@)` must be very similar for the two reactions, since six Co-N bonds are formed in each case. Interestingly however, the equilibrium constant is 100,000 times larger for the second reaction than it is for the first. This is the so called chelate effect: "the enhanced affinity of chelating ligands for a metal ion compared to similar non-chelating (monodentate) ligands for the same metal". The chelate effect is entropy-driven.
Q. Which of the following can be classified as a chelating ligand?

A

`edta^(-4)`

B

`N_(3)^(-)`

C

`PPh_(3)`

D

all of these

Text Solution

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The correct Answer is:
To determine which of the given options can be classified as a chelating ligand, we need to understand the definition of chelating ligands and analyze each option based on that definition. ### Step-by-Step Solution: 1. **Understanding Chelating Ligands**: - Chelating ligands are molecules that can form multiple bonds with a metal ion. They typically have two or more donor atoms that can coordinate to the same metal center, forming a ring-like structure. This multi-dentate nature enhances the stability of the metal-ligand complex. 2. **Analyzing the Options**: - **Option A: EDTA^4-** - EDTA (Ethylenediaminetetraacetic acid) has four carboxylate groups and two amine groups. It can bind to a metal ion through its six donor atoms (two nitrogen atoms and four oxygen atoms from the carboxylate groups). Therefore, EDTA is a chelating ligand. - **Option B: N3^- (Azide ion)** - The azide ion has one nitrogen atom that can coordinate to a metal ion. It can only form one bond, making it a monodentate ligand. Therefore, it is not a chelating ligand. - **Option C: PPh3 (Triphenylphosphine)** - Triphenylphosphine has one phosphorus atom that can coordinate to a metal ion. Like the azide ion, it can only form one bond, making it a monodentate ligand. Therefore, it is not a chelating ligand. - **Option D: All of these** - This option suggests that all the listed ligands are chelating. However, since only EDTA is a chelating ligand, this option is incorrect. 3. **Conclusion**: - Among the options provided, only **EDTA^4-** can be classified as a chelating ligand. ### Final Answer: The correct option is **EDTA^4-**.
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Consider the two complexation equilibria in aqueous solution, between the cobalt (II) ion Co^(2+) (aq) and ethylenediamine (en) on the one hand and ammonia NH_(3) on the other. [Co(H_(2)O)_(6)]^(2+)+6NH_(3)hArr[Co(NH_(3))_(6)]^(2+)+6H_(2)O ...(1) [Co(H_(2)O_(6))]^(2+)+3enhArr[Co(en)_(3)]^(2+)+6H_(2)O ..(2) Electronicaly, the ammonia and en ligands are very similar, since both bond through N and since the liwis base strengths of their nitrogen atoms are similar. This means that DeltaH^(@) must be very similar for the two reactions, since six Co-N bonds are formed in each case. Interestingly however, the equilibrium constant is 100,000 times larger for the second reaction than it is for the first. This is the so called chelate effect: "the enhanced affinity of chelating ligands for a metal ion compared to similar non-chelating (monodentate) ligands for the same metal". The chelate effect is entropy-driven. Q. What may be main reason for reaction (2) having relatively such a large equilibrium constant?

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What is the coordination number of Co in [Co(NH_(3))_(4)(H_(2)O)Br](NO_(3))_(2) ?

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Which complex of the following pairs has the larger value of Delta_(0) (i) [Co(CN)_(6)]^(3-) and [Co(NH_(3))_(6)]^(3+) (ii) [Co(NH_(3))_(6)]^(3+) and [CoF_(6)]^(3-) (iii) [Co(H_(2)O)_(6)]^(2+) and [Co(H_(2)O)_(6)]^(3+) .

What type of isomerism exists in the following pairs of complexes ? (i) [Co(NH_(3))_(5)NO_(3)]SO_(4) and [Co(NH_(3))_(5) SO_(4) ] NO_(3) (ii) [Co(en)(H_(2)O)_(2) Cl_(2)] Cl and [Co(en) (H_(2)O) Cl_(3) ] H_(2)O

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