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Questions
What is the difference between a weak field ligand and a strong field ligand?
Explain the difference between a weak field ligand and a strong field ligand.
Write the difference between a strong field ligand and a weak field ligand.
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Solution
| S.No. | Weak Field Ligand | Strong Field Ligand |
| 1. | A ligand that produces a small splitting of the d-orbitals in the central metal ion. | A ligand that produces a large splitting of the d-orbitals in the central metal ion. |
| 2. | These are the ligands used in octahedral complexes in which the crystal field stabilization energy Δo is less than the pairing energy (P) in a single orbital. | These are the ligands used in octahedral complexes in which the crystal field stabilization energy Δo is greater than the pairing energy (P). |
| 3. | Complexes formed by these ligands are also known as high-spin complexes. | Complexes formed by these ligands are also known as low-spin complexes |
| 4. | The complexes formed are generally paramagnetic. | The complexes formed are mostly diamagnetic or relatively less paramagnetic. |
| 5. | Examples of weak field ligands include I−, Br−, Cl−, and H2O. | Examples of strong field ligands include NH3, CN−, Co. |
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|
Crystal field splitting by various ligands Metal complexes show different colours due to d-d transitions. The complex absorbs light of specific wavelength to promote the electron from t2g to eg level. The colour of the complex is due to the transmitted light, which is complementary of the colour absorbed. The wave number of light absorbed by different complexes of Cr ion are given below:
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Answer the following questions:
(a) Out of ligands "A", "B", "C" and "D", which ligand causes maximum crystal field splitting? Why?
OR
Which of the two, “A” or “D” will be a weak field ligand? Why?
(b) Which of the complexes will be violet in colour? [CrA6]3- or [CrB6]3+ and why?
(Given: If 560 - 570 nm of light is absorbed, the colour of the complex observed is violet.)
(c) If the ligands attached to Cr3+ ion in the complexes given in the table above are water, cyanide ion, chloride ion, and ammonia (not in this order).
Identify the ligand, write the formula and IUPAC name of the following:
- [CrA6]3-
- [CrC6]3+
