Question

Draw a figure to show splitting of degenerate d-orbitals in an octahedral crystal field. How does the magnitude of Δ_o decide the actual configuration of d-orbitals in an complex entity?

Answer 1

When a transition metal ion is placed in an octahedral crystal field (i.e., surrounded by six ligands at the corners of an octahedron), the degenerate (equal-energy) d-orbitals split into two energy levels due to electrostatic interactions between the ligands and the d-electrons.

Energy level splitting the d-orbitals split into

t_2g set (lower energy): d_xy, d_yz, d_xz

e_g set (higher energy): d_z², d_{x² − y²}

Due to face to face repulsion, e_g group of orbitals possesses higher energy than those of t_2g orbitals. The energy gap (crystal field splitting) in between these two sets is Δ_o or 10 Dq.

Role of Crystal Field Splitting Energy (Δ_o or 10 Dq): The magnitude of Δ_o (also called crystal field splitting energy) determines whether electrons will:

• Pair up in the lower energy (t_2g) orbitals: Low-spin configuration (common in strong field ligands like CN⁻, CO).
• Occupy higher energy (e_g) orbitals to avoid pairing: High-spin configuration (common in weak field ligands like F⁻, Cl⁻).