Energy level scheme for square-planar complexes

1 Energy level scheme for square-planar complexes 

A coordinate system for a square-planar complex ML4 (Z 4h symmetry) is displayed in Fig. 8.9.1. The linear combinations of ligand orbitals, matched in symmetry with the metal orbitals, and the molecular orbitals they form, are summarized in Table 8.9.1. A schematic energy level diagram for this type of complexes is given in Fig. 8.9.2. 

Schematic energy level diagram for a square-planar complex ML4. Note the block of levels labelled n is present only for ligands with low-lying it orbitals such as CO, CN, and PR3. 

Symmetry Metal orbital Ligand orbitals Molecular orbitals 

As mentioned in Section 8.3, many square-planar complexes have the d8 configuration. This observation is consistent with the energy level scheme shown in Fig. 8.9.2, with eight electrons occupying the relatively more stable eg, a g, and fog orbitals, and leaving the highly unstable b g level vacant. 

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