Coordination Number 4

Definition

Coordination number 4 refers to the number of ligand atoms that are directly bonded to a central metal atom in a coordination complex. This arrangement is significant as it influences the geometry of the complex, with common shapes being tetrahedral and square planar, each affecting the compound's properties and reactivity.

5 Must Know Facts For Your Next Test

1. The two most common geometries for coordination number 4 are tetrahedral and square planar, depending on factors like the metal's oxidation state and ligand properties.
2. In tetrahedral complexes, ligands are spaced evenly around the central metal atom, leading to bond angles of approximately 109.5°.
3. Square planar complexes typically arise from d8 metal ions, such as nickel(II) or platinum(II), and feature bond angles of 90° between adjacent ligands.
4. Certain ligands can induce different geometries for the same metal center; for example, bidentate ligands can stabilize square planar arrangements.
5. Coordination number 4 is frequently observed in transition metal complexes due to their ability to form multiple bonding interactions with ligands.

Review Questions

• How does coordination number 4 influence the geometry of coordination compounds, and what are the typical geometries associated with this coordination number?
  • Coordination number 4 significantly influences the geometry of coordination compounds by determining how ligands are arranged around the central metal atom. The two primary geometries associated with this coordination number are tetrahedral and square planar. The choice between these geometries often depends on factors such as the metal ion's electronic configuration and the nature of the ligands involved.
• Compare and contrast tetrahedral and square planar geometries in terms of bond angles and examples of metal complexes.
  • Tetrahedral geometry features bond angles of approximately 109.5°, which allows for an even distribution of four ligands around the central atom. In contrast, square planar geometry has bond angles of 90°, resulting in a planar arrangement of four ligands. Common examples include tetrahedral complexes like ext{[CuCl}_4]^{2-} and square planar complexes like ext{[Ni(CN)}_4]^{2-}, highlighting how different geometries can lead to varied properties.
• Evaluate how changes in ligand type can affect the geometry and stability of complexes with a coordination number of 4.
  • The type of ligand has a significant impact on both the geometry and stability of complexes with a coordination number of 4. For instance, bidentate ligands can promote square planar arrangements by forming chelate rings that enhance stability through entropic factors. Additionally, steric and electronic properties of ligands influence whether a tetrahedral or square planar configuration is favored, demonstrating how variations in ligand characteristics can lead to distinct chemical behaviors in these coordination complexes.

Related terms

Ligand: A molecule or ion that donates a pair of electrons to a central metal atom in a coordination complex.

Tetrahedral Geometry: A molecular shape where four atoms or groups are positioned at the corners of a tetrahedron around a central atom, commonly associated with coordination number 4.

Square Planar Geometry: A molecular arrangement where four atoms or groups are positioned at the corners of a square plane around a central atom, another possible configuration for coordination number 4.