Which of the following does not explain the nature of bonding in coordination compounds?

VSEPR Theory

The correct answer is option 4. VSEPR Theory

VSEPR (Valence Shell Electron Pair Repulsion) Theory is a theory used to predict the molecular geometry of molecules, including coordination compounds. It is based on the idea that electron pairs, whether they are bonding or non-bonding, repel each other and arrange themselves in space to minimize repulsion. VSEPR theory is mainly used for molecules with central atoms having a low coordination number (commonly 2, 3, or 4) and primarily focuses on predicting molecular shapes and bond angles.

On the other hand, Crystal Field Theory (CFT), Molecular Orbital Theory (MO Theory), and Valence Bond Theory (VBT) are theories that explain the nature of bonding in coordination compounds:

1. Crystal Field Theory (CFT) describes the interaction between the ligands and the d-orbitals of the central metal ion, leading to the splitting of the d-orbitals into two energy levels (t2g and eg) and giving rise to color and magnetic properties in coordination complexes.

2. Molecular Orbital Theory (MO Theory) combines atomic orbitals of the metal and ligands to form molecular orbitals, providing insights into the nature of covalent bonding in coordination complexes.

3. Valence Bond Theory (VBT) describes the formation of coordinate bonds between the central metal ion and the ligands through the overlap of atomic orbitals.

In summary, VSEPR Theory is not used to explain the nature of bonding in coordination compounds, while CFT, MO Theory, and VBT are specifically designed for this purpose. Therefore, the correct answer is 4. VSEPR Theory.