VBT - The Core Ligand-Strength Benchmark

Trend Order:

$$\text{Strong Field (Pairing): } \text{CO} > \text{CN}^- > \text{en} > \text{NH}_3 \quad \gg \quad \text{H}_2\text{O} > \text{F}^- > \text{Cl}^- > \text{Br}^- > \text{I}^- \text{ :Weak Field (No Pairing)}$$

Concept: Provides a simplified snapshot of the spectrochemical series to correctly determine whether to draw an inner or outer orbital configuration based on whether the ligands induce electron pairing.

Notation:

• $$\text{en}$$ = Ethylenediamine (strong bidentate chelating ligand); $$\text{Halides (F}^-, \text{Cl}^-, \text{Br}^-, \text{I}^-\text{)}$$ = Weak field ligands preserving high-spin states.