The arrangement of ligands around a transition metal ion is the key factor that determines how the d-orbitals split in Crystal Field Theory (CFT).
Effect of Ligand Arrangement
- Octahedral complexes (6 ligands around the metal)
- Six ligands come along the x, y, and z axes.
- Orbitals that point directly at ligands (along the axes) are pushed up in energy.
- Orbitals that lie between axes are less affected and stay lower in energy.
Result: orbitals split into two groups – higher and lower.
- Tetrahedral complexes (4 ligands around the metal)
- Four ligands are placed between the axes.
- Orbitals that lie between axes are pushed up in energy.
- Orbitals that point along the axes face less repulsion, so they stay lower.
Result: splitting pattern is opposite to octahedral, and the energy gap is smaller.
- Square planar complexes (4 ligands in one plane)
- Four ligands are arranged in a flat square.
- One orbital lies directly in the plane pointing at ligands, so it rises the most.
- Others are affected less depending on how they align.
Result: one orbital becomes very high in energy, leading to strong preference for certain electron arrangements (often low-spin, diamagnetic).
- Linear complexes (2 ligands opposite each other)
- Two ligands approach directly opposite along one axis.
- Orbitals pointing along that axis are pushed up strongly.
- Orbitals pointing in other directions are barely affected.
Why this matters
- The pattern of splitting depends directly on geometry.
- This explains:
- Color (different gaps → different light absorbed).
- Magnetism (paired or unpaired electrons).
- Reactivity (which orbitals are available for bonding).
In short:
The way ligands are arranged around the metal decides which d-orbitals are raised or lowered in energy. Different geometries (octahedral, tetrahedral, square planar, linear) give different splitting patterns, which control the properties of the complex.