: 230
VBT Approach: Uses hybridisation to explain geometry and bonding. sp3 = tetrahedral, dsp2 = square planar, d2sp3 = octahedral (inner orbital, low spin), sp3d2 = octahedral (outer orbital, high spin). Inner orbital complexes use (n-1)d orbitals (electrons must pair to free orbitals). Outer orbital complexes use nd orbitals (empty, so existing d-electrons stay unpaired).
VBT Limitations: Cannot quantitatively predict or explain colour. Cannot predict the spectrochemical series. Cannot explain distorted geometries or Jahn-Teller effect. Does not explain why CO and CN- are strong field ligands. The distinction between inner/outer orbital is descriptive, not predictive.
CFT Approach: Treats bonding as electrostatic. Predicts splitting patterns (octahedral, tetrahedral, square planar). Explains colour (d-d transitions), magnetism (CFSE-based spin states), stability trends (Irving-Williams series), and kinetic inertness vs lability.
CFT Limitations: Purely electrostatic assumption ignores covalent character. Cannot explain pi-bonding effects (why CO > CN- > NH3). Cannot account for the nephelauxetic effect (which proves partial covalency). Fails for organometallic compounds.
Ligand Field Theory / MO Theory: Combines the best of both — includes orbital overlap, sigma and pi bonding, and provides a complete molecular orbital energy diagram. Explains both the spectrochemical and nephelauxetic series. Most comprehensive but mathematically complex.