Ligand group orbital approach bonding

Fig. 4.20 The ligand group orbital approach to the bonding in CH4. (a) The 2, 2p, 2py and 2p atomic orbitals of carbon, (b) The four hydrogen H atomic orbitals combine to generate four ligand group orbitals (LGOs).

Fig. 4.24 A partial MO diagram that illustrates the formation of delocalized C—O ir-bonds using the ligand group orbital approach. The CO2 molecule is defined as l5ung on the z axis. The characters of the and 7r MOs are shown in the diagrams at the top of the figure.

Fig. 4.30 A qualitative MO diagram for the formation of Xep2 using a ligand group orbital approach and illustrating the 3c-2e bonding interaction.

Use a ligand group orbital approach to describe the bonding in [NH4]. Draw schematic representations of each of the bonding MOs. 

Fig. 20.12 An approximate MO diagram for the formation of [MLg]"" (where M is a first row metal) using the ligand group orbital approach the orbitals are shown pictorially in Figure 20.11. The bonding only involves M—L fr-interactions.

Initially, we illustrate the ligand group orbital approach by considering the bonding in a linear triatomic XH2 in which the valence orbitals of X are the 25 and 2p atomic orbitals. Let us orient the H—X—H framework so that it coincides with the z axis as shown in Fig. 5.11. Consider the two I5 atomic orbitals of the two H atoms. Each I5 atomic orbital has two possible phases and, when the two Is orbitals are taken as a group, there are two possible phase combinations. These are called ligand group orbitals... 

Dibenzenechromium, like ferrocene, exhibits eclipsed rings in its most stable conformation. The metal-ligand bonding in this compound may be interpreted using the group orbital approach applied to ferrocene earlier in Chapter 5. 

Elfectively, we are transforming the description of the bonding in XH2 from one in which the basis sets are the atomic orbitals of atoms X and H, into one in which the basis sets are the atomic orbitals of atom X and the ligand group orbitals of an H H fragment. This is a valuable approach for polyatomic molecules. 

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