Magnetic orbitals and mechanisms of exchange II.: Superexchange

In a first step, we examine the concept of magnetic orbital which is very useful to treat the mechanism of superexchange. After that, we recall the general broad lines of the first historical model proposed by Anderson. In a second step, we develop a new general treatment for superexchange, in the case of the centrosymmetrical model AXB, where A and B are metal cations and X a common bridging ligand (with here, for simplification, A = B, without transfer between cations). It allows one to retrieve the expression of exchange energy J vs. key molecular integrals, as respectively proposed by several authors such as Anderson on the one hand, Hay, Thibeault, and Hoffmann on the other one, and, finally, Kahn and Briat. This model may be easily generalized to the case where a transfer does exist between both cations, with A = B or A not equal B.