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Chapter 23: Problem 31

(a) What is meant by the term chelate effect? (b) What thermodynamic factor is generally responsible for the chelate effect? (c) Why are polydentate ligands often called sequestering agents?

Short Answer

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(a) The chelate effect is the stabilization of metal-ligand complexes due to the formation of ring-like structures called chelates involving a metal ion and a polydentate ligand, which attaches through multiple donor atoms simultaneously. (b) Entropy is the thermodynamic factor responsible for the chelate effect, as the formation of chelates results in an increase in the number of molecules and overall entropy change. (c) Polydentate ligands are called sequestering agents because they can trap metal ions in stable complexes, protect them from undesirable reactions, and selectively target and remove specific metal ions from solutions, which is essential in various applications.

Step by step solution

01

(a) Definition of chelate effect

The chelate effect is an observed phenomenon in coordination chemistry. It occurs when a polydentate ligand forms a stable complex with a metal ion by attaching to it through multiple donor atoms simultaneously. This formation creates a ring-like structure containing the metal ion, which is called a chelate. The chelate effect stabilizes the metal-ligand complex, making it less reactive and more resistant to substitution reactions.
02

(b) Thermodynamic factor responsible for the chelate effect

The thermodynamic factor responsible for the chelate effect is entropy. When a polydentate ligand forms a chelate with a metal ion, multiple bonds form simultaneously. Consequently, several monodentate ligands are replaced by a single polydentate ligand. This process results in a net increase in the number of molecules in the solution, which leads to an increase in entropy. As the overall entropy change is positive, the chelate formation becomes a thermodynamically favored process.
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(c) Polydentate ligands as sequestering agents

Polydentate ligands are often called sequestering agents because they can "sequester" or "trap" metal ions in a stable complex. Due to the chelate effect, the metal-polydentate ligand complexes are more thermodynamically stable and less reactive compared to their monodentate counterparts. As a result, these complexes can protect metal ions from participating in undesirable reactions and can be used to selectively target and remove specific metal ions from a solution, which is vital in various applications such as water treatment, catalysis, and analytical chemistry.

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Most popular questions from this chapter

Suppose that a transition-metal ion was in a lattice in which it was in contact with just two nearby anions, located on opposite sides of the metal. Diagram the splitting of the metal \(\bar{d}\) orbitals that would result from such a crystal field. Assuming a strong field, how many unpaired electrons would you expect for a metal ion with six \(d\) electrons? (Hint: Consider the linear axis to be the \(z\) -axis)

No compounds are known in which scandium is in the +2 oxidation state. Suggest an explanation.

The complex \(\left[\mathrm{Mn}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}\) contains five unpaired electrons. Sketch the energy-level diagram for the \(d\) orbitals, and indicate the placement of electrons for this complex ion. Is the ion a high-spin or a low-spin complex?

Indicate the coordination number of the metal and the oxidation number of the metal as well as the number and type of each donor atom of the ligands for each of the following complexes: (a) \(\mathrm{Na}_{2}\left[\mathrm{CdCl}_{4}\right]\) (b) \(\mathrm{K}_{2}\left[\mathrm{MoOCl}_{4}\right]\) (c) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right] \mathrm{Cl}\) (d) \(\left[\mathrm{Ni}(\mathrm{CN})_{5}\right]^{3-}\) (e) \(\mathrm{K}_{3}\left[\mathrm{~V}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]\) (f) \(\left[\mathrm{Zn}(\mathrm{en})_{2}\right] \mathrm{Br}_{2}\)

A four-coordinate complex \(\mathrm{MA}_{2} \mathrm{~B}_{2}\) is prepared and found to have two different isomers. Is it possible to determine from this information whether the complex is square planar or tetrahedral? If so, which is it?
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