Orbitals of Octahedrally Based Molecules

Thomas A. Aibright, Jeremy K. Burdett, and Myung-Hwan Whangbo. 

Assembly of the molecular orbital diagram of an octahedral AHg molecule from the orbitals of A and of He- d orbitals are not included on A. 

One way that has been used to produce a localized bonding picture for molecules of this type is to involve the higher energy valence shell d orbitals in bonding. In the Oh point group these transform as Cg + t2g and the result of their inclusion Is shown in 14.2. Now, of course, there are six bonding orbitals and the 

Correlation diagram for the molecular orbital levels of linear AH2, square AH4, and octahedral AHe- The orbital occupancy is that expected for the XeHn systems. Each time two hydrogen atoms are added to the system, two new orbitals are created. For example, on adding two H atoms to AH2, a new ligand-located orbital (big is produced). The dashed lines show how one component of jr, along with one orbital combination from the added H2 give rise to two new orbitals. 

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The molecular orbital model as a linear combination of atomic orbitals introduced in Chapter 4 was extended in Chapter 6 to diatomic molecules and in Chapter 7 to small polyatomic molecules where advantage was taken of symmetry considerations. At the end of Chapter 7, a brief outline was presented of how to proceed quantitatively to apply the theory to any molecule, based on the variational principle and the solution of a secular determinant. In Chapter 9, this basic procedure was applied to molecules whose geometries allow their classification as conjugated tt systems. We now proceed to three additional types of systems, briefly developing firm qualitative or semiquantitative conclusions, once more strongly related to geometric considerations. They are the recently discovered spheroidal carbon cluster molecule, Cgo (ref. 137), the octahedral complexes of transition metals, and the broad class of metals and semi-metals. 

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