Weak and strong field ligands

In summary, the conversation discusses the spectrochemical series of ligands and how it affects the spin and magnetism of octahedral complexes. The left side of the series consists of weak field ligands, while the right side consists of strong field ligands. The person has encountered problems in determining the spin and magnetism of certain complexes, such as [NiF6]2-, which should be high spin according to the ligand F- being weak field but is actually diamagnetic. They use Sidgwick's theory and the effective nuclear charge to explain this phenomenon.
  • #1
Puchinita5
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Homework Statement



So I'm looking at the spectrochemical series of ligands which has that

I- < Br- < Cl- < F- < OH- < ox2- < H20 < NH3 < en <bpy< phen <CN-

Where the left side are weak field ligands and the right side are strong field ligands.

A lot of my homework problems involve me looking at an octahedral complex and deciding whether the complex is low or high spin and then figuring out if the complex is diamagnetic or not.


From problems I have been doing and google searches, I have found that H20 is a weak field ligand and NH3 is strong field.

I can't understand why [NiF6]2- is diamagnetic. F- should be a weak field ligand, which would mean it would lead to a high spin complex. The Ni should have an oxidation state of +4 making it d6, and in a high spin octahedral d6 complex it will not be diamagnetic. It can only be diamagnetic if it was low spin. But why is it low spin if F- is a weak field ligand?

Homework Equations





The Attempt at a Solution

 
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  • #2
Actually We reasoned it out on the basis of Sidgwicks theory. the EAN( effective nuclear charge) it comes out to be 36 corresponding to Krypton
 
Last edited:

1. What are weak and strong field ligands?

Weak and strong field ligands are molecules or ions that bind to a central metal ion in a coordination complex. They are classified based on their ability to cause a splitting of the d-orbitals of the metal ion, known as crystal field splitting.

2. How do weak and strong field ligands affect the properties of a coordination complex?

Weak field ligands cause a small crystal field splitting, resulting in a high-spin complex with unpaired electrons. Strong field ligands, on the other hand, cause a large crystal field splitting, leading to a low-spin complex with paired electrons. This has a significant impact on the magnetic and spectroscopic properties of the complex.

3. What is the relationship between the strength of a ligand and its binding affinity to a metal ion?

The stronger the ligand, the higher its binding affinity to the metal ion. This is because strong field ligands have a greater ability to donate electrons and form stronger bonds with the metal ion compared to weak field ligands.

4. What are some examples of weak and strong field ligands?

Some common examples of weak field ligands include water (H2O), ammonia (NH3), and carbon monoxide (CO). Strong field ligands include cyanide (CN-), nitrite (NO2-), and ethylenediamine (en).

5. How can the strength of a ligand be determined experimentally?

The strength of a ligand can be determined using spectroscopic methods, such as UV-Vis or infrared spectroscopy. The absorption peaks in the spectra can provide information about the energy difference between the split d-orbitals, which is directly related to the strength of the ligand.

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