key term - [Co(NH3)6]3+

Definition

[Co(NH3)6]3+ is a cobalt(III) complex ion where a cobalt ion is coordinated to six ammonia (NH3) ligands, resulting in a positively charged complex. This coordination number of six leads to an octahedral geometry, and the complex exhibits interesting properties such as color and reactivity, particularly in substitution reactions involving its ligands.

5 Must Know Facts For Your Next Test

1. [Co(NH3)6]3+ is typically formed by the oxidation of Co(II) to Co(III) in the presence of ammonia under suitable conditions.
2. The complex displays distinct colors due to electronic transitions between d-orbitals, making it useful in coordination chemistry studies.
3. Ammonia is a neutral ligand and is a strong field ligand, meaning it can create significant splitting of the d-orbitals in the cobalt ion.
4. Substitution reactions involving [Co(NH3)6]3+ can lead to the formation of other complexes, such as [CoCl(NH3)5]2+, showcasing the versatility of the cobalt complex.
5. Kinetics of substitution reactions with [Co(NH3)6]3+ often demonstrate both associative and dissociative mechanisms depending on the entering and leaving ligands.

Review Questions

• How does the structure of [Co(NH3)6]3+ influence its chemical behavior in substitution reactions?
  • [Co(NH3)6]3+'s octahedral structure creates a specific arrangement of ligands around the cobalt center that significantly influences its reactivity. The strong field character of ammonia ligands leads to higher stability and slower kinetics in substitution reactions. However, when substitution does occur, the geometry allows for different pathways, including associative mechanisms that involve an intermediate complex.
• Evaluate the role of ammonia as a ligand in the stability and reactivity of [Co(NH3)6]3+ during substitution reactions.
  • Ammonia acts as a neutral and strong field ligand for [Co(NH3)6]3+, contributing to its stability through effective bonding with cobalt. The ability of ammonia to create significant d-orbital splitting results in a stable electronic configuration. During substitution reactions, ammonia's nature allows for both retention of octahedral geometry and potential reactivity with other ligands, influencing the overall reaction rate and product formation.
• Synthesize information about [Co(NH3)6]3+ to predict how changes in ligand identity might affect its substitution reaction rates and outcomes.
  • Changing the identity of ligands in [Co(NH3)6]3+ can significantly alter both the rates and products of substitution reactions. For instance, substituting NH3 with stronger field ligands like CN- would likely increase stabilization of the cobalt center due to greater d-orbital splitting, resulting in slower substitution kinetics. Conversely, using weaker field ligands such as H2O may increase reactivity due to lower stabilization, leading to faster substitutions and potentially different final complexes based on ligand affinity.

Related terms

Ligand:

A ligand is a molecule or ion that binds to a central metal atom to form a coordination complex, often influencing the complex's properties.

Octahedral Geometry:

A type of molecular geometry where a central atom is surrounded by six ligands at the corners of an octahedron, which is typical for many transition metal complexes.

Substitution Reaction: A chemical reaction where one ligand in a coordination complex is replaced by another ligand, affecting the complex's structure and properties.