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How does crystal field theory describe the attraction between metal ions and ligands?

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Structural diagram of the vitamin B12 coenzyme molecule, highlighting its organometallic core with five nitrogen-cobalt bonds and one cobalt-carbon bond at the center, surrounded by complex organic groups. — coordination compound Coordination compounds contain a central metal atom surrounded by nonmetal atoms or groups of atoms, called ligands. For example, vitamin B₁₂ is made up of a central metallic cobalt ion bound to multiple nitrogen-containing ligands.

Crystal field theory (CFT) describes the attraction between a central metal ion and its surrounding ligands using an electrostatic model. In this framework, ligands are treated as point charges if they are anions, or as point dipoles if they are neutral molecules.12

The theory posits that the stability of a coordination compound is largely derived from the electrostatic attraction between the positively charged metal cation and these negative point charges.32

Beyond this primary attraction, CFT explains the electronic structure of these complexes by considering how the electric field generated by the ligands affects the metal's d orbitals. Because the d orbitals have specific spatial orientations, they experience varying degrees of electrostatic repulsion from the surrounding ligands. This interaction causes the five degenerate d orbitals to split into two or more groups of different energy levels. The specific pattern and magnitude of this crystal field splitting energy depend on the geometric arrangement of the ligands and the strength of the field they generate, which in turn dictates the complex's magnetic, optical, and thermodynamic properties.435