Tetrahedral ligand field splitting

Here we discuss two topics the relationship between octahedral and tetrahedral ligand field splitting parameters, and the pressure-dependence of the octahedral parameter a common feature of these is the use of the AOM to determine the variation of orbital splittings with the intemuclear distance. 

The separation in energy between the ta- and e-orbitals is the tetrahedral ligand field splitting, Aj, where the T denotes tetrahedral. 

Tetrahedral ligand-field splitting values tends to be smaller than corresponding octahedral splitting values, in part because there are fewer ligands to repel electrons in the c/-orbitals in the tetrahedral case. 

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. 

Figure 6. Energy splitting of the d orbitals in octahedral and tetrahedral coordination. The numbers at each level indicate the energy degeneracy that still remains after ligand-field splitting. Note that the energy barycenter (i.e., center of energy ) need not be the same in octahedral and tetrahedral coordination as pictured.

The role of electronic structure in Mn and Co site preference and mobility can to some extent be understood through ligand-field theory (LFT). LET qualitatively explains how the degeneracy of the 3d orbitals is broken when a free TM ion is surrounded by coordinating anions. The ligand-field splitting of d orbitals in octahedral and tetrahedral coordination is pictured in Figure 6. ... 

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. 

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