Tetrahedral complex ligand field splitting

In octahedral complexes, the e -orbitals (dz< and dx2 -yi) lie higher in energy than the t2 -orbitals (dxy, dyz, and dzx). The opposite is true in a tetrahedral complex, for which the ligand field splitting is smaller. 

FIGURE 16.28 Tbe energy levels of the d-orbitals in a tetrahedral complex with the ligand field splitting A,. Each box (that is, orbital) can hold two electrons. The subscript g is not used to label the orbitals in a tetrahedral complex. 

The extension to non-octahedral complexes is possible, but must be carried out with great care The orbitals chosen can be expressed as a linear combination of the usual orbitals for an octahedron, and electron-electron repulsions can then be calculated from those for the octahedral case. It is not necessarily adequate for tetrahedral complexes of the first row transition elements, to use ligand field theory in the strong field limit, even for powerful ligands in V(mesityl)4 the ligand field splitting is only 9250 cm ... 

Table 42 Ligand field splitting parameter A/he (103 cm 1) obtained from the electronic spectra of octahedral and tetrahedral (4C1-) complexes ...

Fig Ligand field splitting patterns for (a) tetrahedral, (b) tetragonally distorted octahedral, and (c) square-planar complexes. 

As the ligand-field splitting of the d orbitals in lower symmetry complexes lead to lower degeneracies and so a need for more parameters to describe them (see Table 6.6), so the d-d transitions of complexes of other than octahedral and tetrahedral geometries can only be discussed by introducing these parameters. For square planar complexes, for instance, two additional parameters must be introduced. 

Make a sketch of a cubic complex (start with a tetrahedral complex and add four ligands). Analyze the repulsion of each of the d orbitals and sketch the splitting pattern that would exist in a cubic field. 

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