The CFT assumes ligands as point charges, leading to the expectation that anionic ligands would have the highest splitting effect. However, this contradicts the observed positioning of anionic ligands at the low end of the spectrochemical series.
According to the crystal field model (CFT), why should anionic ligands exert the greatest splitting effect on d orbitals in coordination compounds?
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In the crystal field model (CFT), the splitting of d orbitals in coordination compounds is influenced by the electrostatic interactions between metal ions and surrounding ligands. Anionic ligands carry negative charge and, being negatively charged, strongly repel the electrons in the metal’s d orbitals. This electrostatic repulsion results in a larger energy gap between the degenerate d orbitals, causing greater splitting. In contrast, neutral ligands have less charge to exert repulsion, leading to smaller energy differences. This stronger electrostatic interaction with anionic ligands enhances the crystal field splitting effect, making them more effective in influencing the electronic structure of the metal center.