Colour of complexes

Need to know

What you need to know

• **Degenerate d-orbitals:** All five have the same energy in a free ion.
• **Octahedral field:** Ligands approach along the axes.
• **e_g orbitals:** $d_{x^2-y^2}$ and $d_{z^2}$ point at ligands, become higher energy.
• **t₂g orbitals:** $d_{xy}$, $d_{xz}$, and $d_{yz}$ point between ligands, become lower energy.

Explanation

The Rainbow of the d-block

1. Split 3d subshell in ligand field — d–d transitions absorb light. | Sim hint: Complementary colour observed.
2. Different ligands → different ΔE → different colours. | Sim hint: Compare [Cu(H₂O)₆]²⁺ blue vs [CuCl₄]²⁻ yellow-green.
3. Degenerate d orbitals split into t₂g and e_g (octahedral). | Sim hint: Electron jumps between split levels.
4. Colourless: d⁰ or d¹⁰ — no d–d transitions (Sc³⁺, Zn²⁺). | Sim hint: Check d electron count.