Side-on interaction

Figure 2.6. End-on and side-on interactions of frontier orbitals of molecular oxygen with orbitals of a metal site. From ref. [32], reproduced with permission of The Electrochemical Society Inc.

O2 interacts with the N4 catalysts usually binding to the d orbitals of the central metal in the macrocyclic stmcture. The energy of the interaction will depend on the energy and the electronic density located on those orbitals. Figure 7.16 illustrates some different possible interactions (end-on and side-on) of the orbitals of the oxygen molecule with the orbitals of the metal in the M-N4 molecule for end-on and side-on interactions, respectively. 

Figure 1.13. Packing arrangement for C6o(ferrocene)2 showing the side-on interactions. (Reproduced by permission of The Royal Society of Chemistry, from ref 75.)...

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