Coordination Number 6

Definition

Coordination number 6 refers to the number of ligand atoms that are directly bonded to a central metal ion in a coordination complex. This arrangement typically leads to an octahedral geometry, which is one of the most common structural types in coordination chemistry, impacting both the properties and behaviors of these complexes.

5 Must Know Facts For Your Next Test

1. Complexes with a coordination number of 6 often exhibit octahedral geometry, where six ligands surround the central metal ion.
2. Common ligands that can achieve coordination number 6 include water (H2O), ammonia (NH3), and halides like chloride (Cl-).
3. Transition metals such as iron (Fe), cobalt (Co), and nickel (Ni) frequently form coordination complexes with a coordination number of 6.
4. The electronic configuration of the central metal ion plays a significant role in determining the stability and reactivity of the coordination complex.
5. Coordination number 6 is prevalent in many biological systems, including metalloenzymes and hemoglobin, influencing their function.

Review Questions

• How does the coordination number of 6 influence the geometry and stability of coordination compounds?
  • The coordination number of 6 typically results in an octahedral geometry, where six ligand atoms are symmetrically arranged around the central metal ion. This arrangement not only maximizes the spatial efficiency of the ligands but also enhances the stability of the complex due to optimal overlap between the ligand orbitals and the metal's d-orbitals. As a result, coordination number 6 is commonly observed in stable transition metal complexes.
• Compare the properties of complexes with different coordination numbers, focusing on those with coordination number 6 versus those with lower coordination numbers.
  • Complexes with coordination number 6 usually exhibit octahedral geometry and enhanced stability compared to those with lower coordination numbers like 4 or 2. For example, tetrahedral complexes (coordination number 4) may show greater reactivity due to less steric hindrance around the central metal ion. In contrast, coordination number 6 complexes often have stronger metal-ligand interactions because of more available bonding sites, leading to distinct spectroscopic and magnetic properties.
• Evaluate the significance of coordination number 6 in biological systems and its impact on biochemical processes.
  • Coordination number 6 plays a critical role in biological systems, particularly in metalloenzymes and hemoglobin. In hemoglobin, the iron ion has a coordination number of 6, allowing it to bind oxygen molecules effectively. This specific arrangement is crucial for oxygen transport in the bloodstream. Additionally, many enzymes utilize transition metals with coordination number 6 for catalysis, as it helps stabilize reaction intermediates and facilitates electron transfer processes vital for metabolic pathways.

Related terms

Ligand: A ligand is a molecule or ion that donates a pair of electrons to a central metal ion in a coordination compound, forming a coordinate bond.

Octahedral Geometry:

Octahedral geometry is a molecular shape with six ligand atoms symmetrically arranged around a central atom, resembling two square pyramids joined at their bases.

Coordination Complex: A coordination complex is a compound consisting of a central metal atom bonded to surrounding ligands, which can be neutral molecules or ions.