Ligand Field Theory (LFT) explains the electronic structure of square planar complexes by looking at how the metal d-orbitals interact with ligands in this geometry. Here’s a explanation:
1. Geometry
- Square planar complexes usually form with d⁸ metal ions like Pt²⁺, Pd²⁺, and Ni²⁺.
- The four ligands are arranged at the corners of a square around the metal.
2. d-Orbital Splitting
- In a square planar field, the d-orbitals split differently compared to octahedral or tetrahedral complexes:
- The orbital pointing directly at the ligands (dx²–y²) has the highest energy because of strong repulsion.
- The other orbitals (dz², dxy, dxz, dyz) have lower energies, with dz² slightly higher than the rest.
3. Electron Configuration
- For a d⁸ metal ion:
- The lower-energy d-orbitals are fully filled.
- The dx²–y² orbital remains empty, which makes the complex diamagnetic (no unpaired electrons).
4. Why LFT Helps
- LFT shows why square planar geometry is preferred over tetrahedral for d⁸ metals:
- Filling the lower-energy orbitals maximizes stability.
- It also explains:
- Magnetism: square planar d⁸ complexes are usually diamagnetic.
- Reactivity: empty dx²–y² orbital allows ligand substitution reactions.
In short:
- LFT predicts d-orbital energies in square planar geometry.
- Explains why d⁸ metals prefer square planar, why they are diamagnetic, and how they react.