key term - Coordination Number 4

Definition

Coordination number 4 refers to the number of ligand atoms that are directly bonded to a central metal ion in a coordination complex. This geometric arrangement significantly influences the properties and behavior of the compound, including its stability, reactivity, and color. The coordination number also relates to the spatial arrangement of ligands around the central ion, which can lead to different shapes such as tetrahedral or square planar configurations.

5 Must Know Facts For Your Next Test

1. Coordination number 4 can lead to different geometrical arrangements, primarily tetrahedral and square planar, depending on factors like the type of ligands and the central metal ion's electron configuration.
2. In tetrahedral complexes, the bond angles are approximately 109.5°, while in square planar complexes, the bond angles are 90° and 180°.
3. Certain metal ions prefer a coordination number of 4 due to their electronic structure; for example, transition metals like nickel and platinum commonly exhibit this coordination.
4. The properties of coordination compounds with a coordination number of 4 can vary widely, influencing their magnetic properties and color due to ligand field effects.
5. Coordination number impacts the reactivity and stability of complexes, as it affects how ligands interact with the central metal ion.

Review Questions

• Compare and contrast the geometric arrangements associated with coordination number 4 and explain how they influence the properties of coordination compounds.
  • Coordination number 4 can lead to two main geometric arrangements: tetrahedral and square planar. In tetrahedral complexes, ligands are positioned at the corners of a tetrahedron, resulting in bond angles of about 109.5°. In contrast, square planar complexes have ligands arranged in a flat square plane with bond angles of 90° and 180°. These geometries influence the properties of the compounds, such as their magnetic behavior and color due to differences in ligand field splitting.
• Evaluate how different types of ligands can affect the stability and reactivity of coordination compounds with a coordination number of 4.
  • The type of ligands attached to a central metal ion significantly influences the stability and reactivity of coordination compounds with a coordination number of 4. Strong-field ligands can create larger splitting in energy levels, affecting electronic transitions and thus color and magnetic properties. Weak-field ligands may result in smaller splitting, potentially leading to increased reactivity due to higher energy availability for chemical reactions. The choice of ligand not only impacts geometric arrangement but also determines how stable or reactive the complex will be under various conditions.
• Analyze the role of coordination number in determining the electronic structure and properties of transition metal complexes.
  • Coordination number plays a crucial role in shaping the electronic structure and properties of transition metal complexes. For coordination number 4, whether in a tetrahedral or square planar geometry, it affects how electrons are distributed among d-orbitals due to ligand field theory. The arrangement influences energy splitting between these orbitals, impacting magnetic properties—such as whether the complex is paramagnetic or diamagnetic—and absorption characteristics that determine color. This relationship highlights how coordination numbers are essential for understanding not just structural aspects but also functional behavior in chemistry.

Related terms

Ligands:

Molecules or ions that donate electron pairs to a central metal ion to form coordination complexes.

Tetrahedral Complex: A type of coordination geometry where four ligands are arranged around a central metal ion at the corners of a tetrahedron.

Square Planar Complex: A type of coordination geometry where four ligands are arranged around a central metal ion in a flat square plane.