Ligand nonbonding

Recent SCF—XaSW calculations indicate that the above geometry is stabilized by attractive ligand-ligand nonbonded interactions231, 232 ... 

In fact, rather than considering the metal d orhitals individually, we must form new combinations that either avoid the six ligands (nonbonding orbitals) or point towards them (antibonding orbitals). These linear combinations, which allow the original orbitals to be reoriented, are indicated below and shown graphically in Figure 2.5. 

Chapter 5. The Concept of Natural Ligand Nonbonded Repulsion. The Ethane Paradigm. 

MOMEC is a force field for describing transition metal coordination compounds. It was originally parameterized to use four valence terms, but not an electrostatic term. The metal-ligand interactions consist of a bond-stretch term only. The coordination sphere is maintained by nonbond interactions between ligands. MOMEC generally works reasonably well for octahedrally coordinated compounds. 

Two qualitative models have been successful in accounting for many of the structural changes in sulfoxides and sulfones5. One is the Faience Shell Electron Pair Repulsion (VSEPR) theory8, while the other approach involves considerations of nonbonded ligand/ligand interactions9. 

Finally, note that no combination of ligand a orbitals interacts with members of the metal t2g set. The vanishing overlap between any ligand a orbital and, say, the dxy orbital is illustrated in Fig. 6-8. Overall, therefore, the metal t2g orbitals are nonbonding in this scheme. Recall how the 2p orbital of oxygen is similarly nonbonding to the hydrogen orbitals in water. 

---