Crystal Field Theory (CFT) is a model used to explain the behavior of transition metal complexes. It describes how the presence of ligands (molecules or ions attached to the metal) affects the energy of the metal’s d-orbitals.
Key Ideas of CFT:
- Metal–ligand interaction
- In a free metal ion, all five d-orbitals have the same energy.
- When ligands approach, their negative charges (or electron pairs) repel the electrons in the d-orbitals.
- This repulsion is not equal, so the d-orbitals split into groups of higher and lower energy.
- Orbital splitting
- The pattern of splitting depends on the geometry of the complex:
- Octahedral (most common)
- Tetrahedral
- Square planar, etc.
- The pattern of splitting depends on the geometry of the complex:
- Consequences of splitting
- The way electrons fill the orbitals (high-spin vs. low-spin) determines:
- Color of complexes (due to light absorption for d–d transitions).
- Magnetism (paramagnetic with unpaired electrons vs. diamagnetic with all paired).
- Reactivity and stability of the complex.
- The way electrons fill the orbitals (high-spin vs. low-spin) determines:
Why CFT is important:
- Explains why transition metal complexes have such brilliant colors.
- Predicts whether a complex will be magnetic or not.
- Helps in understanding catalysis, bioinorganic chemistry, and material properties.
In simple terms:
Crystal Field Theory explains how ligands around a transition metal cause its d-orbitals to split into different energy levels, and how this splitting governs the color, magnetism, and stability of the complex.