Mekanisme Reaksi Senyawa Kompleks - MK Kimia Koordinasi

Summary

This lecture on coordination chemistry delves into the mechanisms of electron transfer in complex compounds. It contrasts two primary mechanisms: outer sphere and inner sphere electron transfer, highlighting their differences. The outer sphere mechanism involves electron transfer across solvent spaces, while the inner sphere mechanism occurs via ligands in the coordination sphere. The lecture further explores ligand substitution mechanisms, including dissociative, associative, and interchange types. Factors like ion size and ligand properties influence these processes. Additionally, it touches on kinetic studies and conjugate base mechanisms, aiming to enhance understanding of chemical reactions involving coordination compounds.

Takeaways

• 😀 The lecture focuses on mechanisms in coordination chemistry, particularly electron transfer and ligand substitution mechanisms.
• 😀 Electron transfer mechanisms can be categorized into two types: outer sphere and inner sphere.
• 😀 In outer sphere mechanisms, electron transfer occurs through space or solvent between metal ions without involving ligands.
• 😀 In inner sphere mechanisms, electron transfer is facilitated by ligands within the coordination sphere, with ligands acting as bridges.
• 😀 A key distinction between outer and inner sphere mechanisms is whether the electron transfer involves ligands (inner sphere) or not (outer sphere).
• 😀 The Marcus theory is used to explain how ion size differences impact the electron transfer process, particularly in redox reactions.
• 😀 A change in the size of metal ions during redox reactions leads to adaptation in the bond length, geometry, and coordination environment.
• 😀 Ligand substitution mechanisms include dissociation, association, and interchange, each with different processes for ligand replacement.
• 😀 Dissociative substitution involves the removal of a ligand before a new ligand can bind, leading to an intermediate with a lower coordination number.
• 😀 Associative substitution involves the binding of a new ligand before the departure of the old ligand, creating an intermediate with a higher coordination number.
• 😀 Interchange substitution mechanisms occur simultaneously, where bond formation and breaking happen at the same time, creating a transition state.
• 😀 Kinetics of dissociation and association reactions involve determining the rate laws for each mechanism, with dissociation following first-order kinetics and association second-order kinetics.

Q & A

What are the two types of electron transfer mechanisms discussed in the video?

The two types of electron transfer mechanisms discussed are the outer sphere mechanism and the inner sphere mechanism.

How does the outer sphere mechanism differ from the inner sphere mechanism in electron transfer?

In the outer sphere mechanism, the electron transfer occurs directly through space or through the solvent between two metal ions. In the inner sphere mechanism, the electron transfer is facilitated through the ligand within the coordination sphere of the complex.

Can you provide an example of the outer sphere mechanism?

An example of the outer sphere mechanism is the transfer of electrons between iron (Fe) and ruthenium (Ru) in a complex such as Fe(CN)6^3- and Ru(NH3)6^2+ where the electron transfer occurs without changing the ligands.

What does the Marcus theory explain in the context of outer sphere electron transfer?

The Marcus theory explains how changes in ion size during redox reactions influence the electron transfer process. It suggests that ion size changes, such as the transition from Fe2+ to Fe3+, require adjustments in bond lengths or angles to facilitate the electron transfer.

What is the role of ligands in the inner sphere electron transfer mechanism?

In the inner sphere mechanism, the electron transfer occurs through a ligand that bridges the metal ions. This means that the ligand facilitates the electron transfer between the metal centers.

Can you give an example of the inner sphere electron transfer mechanism?

An example of the inner sphere mechanism is the electron transfer between Cr2+ and Co3+ in a complex involving ligands like chloride ions (Cl-) where chloride acts as a bridge in the transfer process.

What are the three main types of ligand substitution mechanisms described in the video?

The three main types of ligand substitution mechanisms are dissociative, associative, and interchange.

How does the dissociative mechanism of ligand substitution work?

In the dissociative mechanism, the ligand is first dissociated from the metal complex, forming an intermediate with a lower coordination number. Afterward, a new ligand can bind to the metal ion.

What is the key difference between interchange dissociative (ID) and interchange associative (IA) mechanisms?

In interchange dissociative (ID), the bond between the metal and the original ligand weakens before the new ligand binds, while in interchange associative (IA), the new ligand binds first before the old ligand dissociates.

What factors can promote the dissociative mechanism of ligand substitution?

Factors that can promote the dissociative mechanism include the electronic configuration of the metal center (such as D6 or D8) and the presence of large ligands that create steric hindrance, destabilizing the complex and facilitating dissociation.