Octahedral complexes, molecular

Fig. 2. Simplified molecular orbital diagram for a low spia octahedral complex, such as [Co(NH3 )g, where A = energy difference a, e, and t may be antisymmetric (subscript ungerade) or centrosymmetric (subscript, gerade) symmetry orbitals. See text.

Figure 19.14 Molecular orbital diagram for an octahedral complex of a first series transition metal (only a interactions are considered in this simplified diagram).

FIGURE 16.36 I1ie tear-shaped objects are representations of the six ligand atomic orbitals that are used to build the molecular orbitals of an octahedral complex in ligand field theory. They might represent s- or p-orbitals on the ligands or hybrids of the two. 

We are now ready to apply the ideas in the preceding three sections to the construction of molecular orbitals in octahedral complexes. 

The formation of dimeric products is unique for the case of boron, because analogous complexes with other elements are all monomeric [95]. This can be attributed to the small covalent radius of the boron atom and its tetrahedral geometry in four-coordinate boron complexes. Molecular modeling shows that bipyramidal-trigonal and octahedral coordination geometries are more favorable for the formation of monomeric complexes with these ligands. 

Fig. 4.4 Molecular orbital diagram for octahedral complexes (cr-interaction only)...

FIGU RE 17.14 The coordinate system to designate orbitals used in constructing molecular orbitals for an octahedral complex. 

When describing a complex in terms of molecular orbitals, we need to establish a model by which we can identify the orbitals utilized by both the metal and the ligands. We will first consider an octahedral complex with the positions of the ligands identified on the coordinate system shown in Figure 17.14, and the orbitals will be designated by the numbers assigned to the ligands in the positions indicated. 

FIGURE 17.16 Ihe molecular orbital energy level diagram for an octahedral complex. 

Although we will not write the complete wave functions as we did for the case of an octahedral complex, the molecular orbitals give rise to the energy level diagram shown in Figure 17.20. 

FIGURE 18.9 Interpretation of M—charge transfer absorption in an octahedral complex using a modified molecular orbital diagram.The transitions are from e or t2g orbitals on the metal to orbitals on the ligands. 

Swanson, B. I. and S. K. Satija. 1977. Molecular vibrations and reaction pathways. Minimum energy coordinates and compliance constants for some tetrahedral and octahedral complexes. J. Am. Chem. Soc. 99 987-991. 

The molecular orbital model can also be applied to complexes of the d-block elements. In octahedral complexes the d-orbitals of the metal are not degenerate, as they are in the free metal, because of the interaction between the ligand and metal orbitals. The five d-orbitals are split into three t2g (nonbonding) and two e (antibonding) MOs that is ... 

A representative molecular orbital diagram for an octahedral d-block metal complex ML6 is shown in Figure 1.8. The MOs are classified as bonding (oL and ttL), nonbonding (jtM) and antibonding (o, nl and ). The ground-state electronic configuration of an octahedral complex... 

Although outside the main thrust of the book, attention should be drawn to the important use that octahedral complexes are receiving as molecular probes. Metal complexes can sometimes recognize specific sites on biological material. The array of isomeric forms possible with some metal complexes (previous section) adds a dimension to their use as probes. 

Figure 2.21 Relative molecular orbital energies of an octahedral complex ML. (o-bonding with the ligands).

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