Spectrochemical series

The spectrochemical series is a term from the ligand field theory. It assigns different ligands according to their ability to split the d- orbitals of a metal atom energetically. The spectrochemical series of the ligands were prepared in 1938 by Japanese chemist R. Tsuchida.

  • 2.1 Criteria for the classification of the metals in the series
  • 4.1 references

Spectrochemical series of ligands

The number in the left-wing ligands produce a weak ligand field splitting and synchronization and can be viewed as a weak Lewis base.

The farther right are the ligand, the greater their generated ligand field splitting, which has on the one hand affect the color of a complex, is the other cause of the formation of a high-spin or low-spin complex.

Accordingly, the ligands can be seen as a strong Lewis bases on the right side relative to the left-wing.

Criteria for the classification of the ligands in the series

  • Electronegative ligands results in a lower division, as they take the electron density from the central particle and thus the interaction between the electrons is reduced. Also result in a smaller more ligands of the ligand field splitting as their electrons are distributed in a larger volume.
  • From the molecular orbital theory can be a connection with the ability of a ligand to build a pi- back-bonding and derive the splitting of the d orbitals in the complex.

Spectrochemical series of metal ions

The ligand field splitting also depends on the metal cation. The higher the charge of the metal cation, the higher is the splitting and the sooner low-spin complexes form. The in this series left standing metal ions cause a small ligand field splitting and are still usually high-spin complexes. The standing right cause a high splitting and are still usually low-spin complexes.

Criteria for the classification of the metals in the series

A higher oxidation state of the central particle has a direct influence on the ligands, which are thus the central particle closer. The electrostatic repulsion between the electrons and the ligand d electrons of the central particle is increased.

For example, nickel complexes

A criterion for the strength of the splitting, the geometry in four-coordinate complexes dar. Here are both tetrahedral and square-planar geometry possible:

  • For nickel (II ) complexes are formed in strongly segregating ligand square-planar and tetrahedral in less splitting ligand coordination polyhedra from.
  • If one considers, however, nickel tetracarbonyl, one is in spite of the strong splitting carbonyl ligands define a tetrahedral geometry. The splitting of nickel ( 0) is too weak here.
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