where P is the pairing energy and δ HS = 1 for high‑spin, 0 for low‑spin. To go beyond the textbook description, we propose the BETTER acronym as a checklist for analyzing any transition‑metal complex:
[ K_\textSCO = \frac[HS][LS] = \exp\left(-\frac\Delta G^\circRT\right) = \exp\left(-\frac\Delta H^\circ - T\Delta S^\circRT\right) ] K Kumar Inorganic Chemistry Pdf 179 BETTER
The series is not static; and relativistic effects (especially for 4d/5d metals) shift the ordering. Recent synchrotron experiments show that π‑backbonding can increase Δ beyond the textbook values for CO‑bound low‑spin complexes. 2.3 Ligand‑Field Theory (Molecular‑Orbital Perspective) LFT treats metal–ligand bonding as a mixing of metal d orbitals with ligand symmetry‑adapted linear combinations (SALCs). The e g set (dx²‑y², dz²) interacts strongly with σ‑donor SALCs, while the t 2g set (dxy, dxz, dyz) participates in π‑backbonding when ligands possess low‑lying π* orbitals (e.g., CO, CN⁻). The Ligand‑Field Stabilization Energy (LFSE) can be expressed as: where P is the pairing energy and δ