Antiferromagnetic exchange pathway

Fig. 1. Exchange pathways (a) antiferromagnetic superexchange by way of a single bridge orbital, (b) a molecular orbital viewpoint for a, (c) ferromagnetic superexchangc by way of two orthogonal bridge orbitals.

If several exchange pathways exist in polynuclear coordination complexes, ferromagnetic and antiferromagnetic pathways can compete for a given spin dimer, usually resulting in a dominant antiferromagnetic exchange. 

The analysis we have made is clearly qualitative however, it explains well almost all the experimental results reported in the literature. When the number of exchange pathways leads to ferromagnetic and antiferromagnetic contributions that are very close in magnitude, a small variation of the M - N - C angle and the nature of the M and M metal ions start to be the important factors that determine the nature of the exchange interaction. 

As shown in the above examples, several attractive situations, related to some typical combinations of the metal ions, may be investigated in particular from the viewpoint of the spin dimensionality and the nature of the exchange pathways [5-11]. Obviously, the binuclear systems present the simplest examples for studying exchange interactions, as reported in several review papers. They are commonly characterized by an antiferromagnetic coupling between... 

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