Coordination Number 4

Definition

Coordination number 4 refers to the number of ligand atoms that are bonded to a central metal atom in a coordination complex. This configuration can influence the geometry of the complex, leading to various arrangements such as tetrahedral or square planar structures, which are essential in understanding the bonding and behavior of coordination compounds.

5 Must Know Facts For Your Next Test

1. Coordination number 4 is often observed in transition metal complexes, reflecting the versatility and bonding capabilities of these metals.
2. In tetrahedral complexes, ligands are arranged at angles of approximately 109.5°, while in square planar complexes, the angles between ligands are 90° and 180°.
3. The geometry adopted by a coordination complex with a coordination number of 4 can be influenced by factors like the nature of the metal ion, the size of the ligands, and electronic effects.
4. Some common examples of metal complexes with coordination number 4 include nickel(II) complexes and certain platinum(II) compounds.
5. The choice between tetrahedral and square planar geometries often depends on the ligand field strength and steric considerations surrounding the central metal.

Review Questions

• How does coordination number 4 influence the geometrical arrangement of ligands around a central metal atom?
  • Coordination number 4 allows for two primary geometrical arrangements: tetrahedral and square planar. In tetrahedral geometry, ligands occupy positions that minimize repulsion, leading to angles of about 109.5°. Conversely, in square planar geometry, ligands are arranged at right angles and opposite each other, creating a more planar structure. The specific arrangement adopted depends on several factors including the identity of the metal and its electronic environment.
• Compare and contrast tetrahedral and square planar geometries in terms of their bond angles and steric implications.
  • Tetrahedral geometry has bond angles close to 109.5°, resulting from four ligands being symmetrically spaced in three-dimensional space. This arrangement minimizes steric hindrance among larger ligands. On the other hand, square planar geometry features bond angles of 90° and 180°, which may lead to increased steric interactions if larger ligands are present. The choice between these geometries is often influenced by ligand size and electronic effects within the coordination complex.
• Evaluate how factors like ligand type and central metal ion influence the preferred geometry for complexes with coordination number 4.
  • The preferred geometry for coordination number 4 complexes is influenced by several factors including the nature of the central metal ion and the types of ligands involved. For example, stronger field ligands tend to favor square planar arrangements due to their ability to stabilize such geometries through ligand field theory. Additionally, if the central metal ion has d8 electron configuration, it commonly adopts square planar geometry, while d10 configurations typically prefer tetrahedral shapes. This interplay between metal characteristics and ligand properties ultimately dictates the geometric outcome of the complex.

Related terms

Ligands: Molecules or ions that can donate electron pairs to a central metal atom, forming coordinate covalent bonds.

Tetrahedral Geometry: A molecular shape characterized by four substituents around a central atom arranged at the corners of a tetrahedron, typically associated with coordination number 4.

Square Planar Geometry: A molecular shape where four ligands are positioned at the corners of a square plane around a central atom, another common arrangement for coordination number 4.