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💏intro to chemistry review

K3[Fe(CN)6]

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

K3[Fe(CN)6], also known as potassium ferrocyanide, is a coordination compound consisting of a central iron(III) ion surrounded by six cyanide ligands. It is an important compound in the field of coordination chemistry, particularly in the study of transition metal complexes.

5 Must Know Facts For Your Next Test

  1. The central iron(III) ion in K3[Fe(CN)6] has a +3 oxidation state, and the six cyanide ligands are arranged in an octahedral geometry around the iron.
  2. The cyanide ligands in K3[Fe(CN)6] are strong-field ligands, meaning they cause a large splitting of the d-orbitals in the metal ion, resulting in a low-spin configuration.
  3. K3[Fe(CN)6] is a stable, water-soluble compound that is commonly used as a reagent in various analytical and synthetic applications.
  4. The intense blue color of the K3[Fe(CN)6] solution is due to the electronic transitions within the coordination complex, which are influenced by the ligand field.
  5. The ferrocyanide ion, [Fe(CN)6]3-, is an important building block in the synthesis of other coordination compounds and is used in the production of Prussian blue pigment.

Review Questions

  • Explain the structure and bonding in the K3[Fe(CN)6] coordination complex.
    • The K3[Fe(CN)6] coordination complex consists of a central iron(III) ion (Fe3+) surrounded by six cyanide ligands (CN-) in an octahedral arrangement. The cyanide ligands are strong-field ligands, meaning they cause a significant splitting of the d-orbitals in the iron ion, resulting in a low-spin configuration. The iron-cyanide bonds are primarily covalent in nature, with the iron donating electron density to the cyanide ligands through sigma and pi bonding interactions. This results in a stable, water-soluble coordination complex with a distinctive blue color due to the electronic transitions within the complex.
  • Discuss the importance of K3[Fe(CN)6] in the context of coordination chemistry and its applications.
    • K3[Fe(CN)6] is an important compound in the field of coordination chemistry as it serves as a model system for understanding the properties and behavior of transition metal complexes. The ferrocyanide ion, [Fe(CN)6]3-, is a versatile building block used in the synthesis of other coordination compounds and is a key component in the production of Prussian blue pigment. Additionally, K3[Fe(CN)6] has various analytical and synthetic applications, such as in redox titrations, as a complexing agent, and as a precursor for the preparation of other iron-containing compounds. The study of the structure, bonding, and electronic properties of K3[Fe(CN)6] provides valuable insights into the fundamental principles of coordination chemistry and the reactivity of transition metal complexes.
  • Evaluate the role of the cyanide ligands in the stability and properties of the K3[Fe(CN)6] coordination complex.
    • The cyanide ligands (CN-) play a crucial role in the stability and properties of the K3[Fe(CN)6] coordination complex. As strong-field ligands, the cyanide ions cause a significant splitting of the d-orbitals in the central iron(III) ion, resulting in a low-spin configuration. This electronic configuration contributes to the high stability of the complex, as the low-spin state is energetically favorable. Additionally, the covalent nature of the iron-cyanide bonds, with both sigma and pi bonding interactions, further enhances the stability of the complex. The presence of the cyanide ligands also influences the electronic transitions within the complex, leading to the distinctive blue color observed in K3[Fe(CN)6] solutions. The unique properties of the cyanide ligands, such as their ability to form strong, stable complexes with transition metals, make K3[Fe(CN)6] an important compound in the study of coordination chemistry and its applications.