Chemistry · Ch 5 — Coordination Chemistry
Crystal Field Splitting in Octahedral Complexes
Crystal Field Splitting in Octahedral Complexes
In an octahedral field, six ligands approach the central metal ion along the +x, -x, +y, -y, +z and -z axes. The two orbitals lying directly along these axes, dx²-y² and dz², experience strong, direct repulsion from the incoming ligands and rise sharply in energy, while the three orbitals with lobes directed BETWEEN the axes, dxy, dyz and dzx, are repelled less and rise only slightly (or fall relative to the axial pair). To keep the average (barycentre) energy of all five orbitals unchanged, the higher-energy pair -- labelled eg (dx²-y², dz²) -- rises by 3/5 Δ₀ above the barycentre, while the lower-energy trio -- label …
What this figure shows. A central metal ion at the origin of an x-y-z coordinate system enclosed in a transparent cube, with six ligands L1-L6 approaching along the +x, -x, +y, -y, +z and -z axes. Superimposed at the centre are the five d orbital lobes in different colours: the dz² and dx²-y² lobes point directly along the axes toward the incoming ligands L1-L6, while the dxy, dyz and dxz lobes point diagonally, between the axes, away from the direct line of ligand approach -- visually showing why the axia …
What this figure shows. An energy-level diagram with three stages read left to right: on the far left, the five d orbitals of the free gaseous ion, all at one degenerate energy level; in the middle, a dashed horizontal line marking the raised 'average energy of the d orbitals in a spherical crystal field' (all five still degenerate, but now higher than the free-ion level); on the right, the same average-energy line with the five orbitals split into two groups -- the eg pair (dx²-y², dz²) raised by 3/5 Δ₀ above the average, and the t2g trio (dxy, dyz, dxz) lowered by 2/5 Δ₀ below the average -- with Δ₀ marked as …