key term - High-spin complex

Definition

A high-spin complex is a type of coordination compound characterized by the presence of unpaired electrons in its d-orbitals due to weak field ligands that do not cause significant splitting of the d-orbital energies. In high-spin complexes, the electrons occupy the higher energy orbitals before pairing up, which is typical for transition metals with larger crystal field splitting energy (Δ) values. This results in a greater number of unpaired electrons and impacts the magnetic and spectral properties of the complex.

5 Must Know Facts For Your Next Test

1. High-spin complexes are more likely to be formed with weak field ligands such as halides (e.g., Cl\(^-"), Br\(^-") and I\(^-").
2. The presence of unpaired electrons in high-spin complexes results in paramagnetism, making these complexes attracted to magnetic fields.
3. High-spin configurations usually occur in transition metals with fewer than half-filled d-orbitals, often found in the first-row transition metals.
4. The crystal field splitting energy (Δ) is less than the pairing energy in high-spin complexes, allowing electrons to occupy higher energy orbitals without pairing.
5. High-spin complexes exhibit distinct spectral properties that can be analyzed through techniques such as UV-Vis spectroscopy, revealing information about their electronic transitions.

Review Questions

• Compare and contrast high-spin complexes with low-spin complexes in terms of their electronic configurations and the types of ligands involved.
  • High-spin complexes have unpaired electrons due to weak field ligands, allowing electrons to occupy higher energy d-orbitals before pairing. In contrast, low-spin complexes feature strong field ligands that cause a significant splitting of d-orbitals, leading to electron pairing in lower energy orbitals. This difference affects their magnetic properties, with high-spin complexes being paramagnetic and low-spin complexes often exhibiting diamagnetism.
• Discuss how the choice of ligands affects the formation of high-spin versus low-spin complexes and provide examples.
  • The choice of ligands plays a crucial role in determining whether a coordination complex will be high-spin or low-spin. Weak field ligands such as Cl\(^-") or Br\(^-") lead to high-spin configurations because they produce small crystal field splitting (Δ), allowing unpaired electrons. Conversely, strong field ligands like CN\(^-") or CO create large splitting energies that favor low-spin configurations by promoting electron pairing in lower energy orbitals. For instance, [FeCl\(_6\)]\(^{3-}\) is typically high-spin, while [Fe(CN)\(_6\)]\(^{3-}\) is low-spin.
• Evaluate the implications of having a high number of unpaired electrons in high-spin complexes on their reactivity and applications in chemistry.
  • Having a high number of unpaired electrons in high-spin complexes significantly impacts their reactivity and applications. The presence of unpaired electrons contributes to greater magnetic properties, making these complexes useful in magnetic resonance imaging (MRI) and as catalysts in various chemical reactions due to their ability to participate in redox processes. Additionally, their unique electronic transitions can be harnessed in photochemistry and material science. Understanding how these unpaired electrons affect stability and interaction with other molecules is crucial for designing new materials and catalysts.

Related terms

Ligands:

Molecules or ions that bind to a central metal atom in a coordination complex, influencing its electronic properties and stability.

Crystal Field Theory:

A model that describes the electronic structure of transition metal complexes by considering the interaction between the central metal ion and surrounding ligands, leading to splitting of d-orbitals.

Low-spin complex: A type of coordination complex where electrons pair up in lower energy orbitals before occupying higher ones, typically formed with strong field ligands.