Theory of Superexchange for 3dn-Ions (1≤n≤9) involved in natural and artificial magnets I — setting the problem

In this part labelled I we extend a general treatment of superexchange previously published in the case of 3d¹-metallic cations appearing in the centrosymmetrical toy model AXB. The orbitals of cations A and B are always of d- type whereas that of the diamagnetic ligand X is of s- or p- type. In the present article we consider the general case of 3d^pi -mctallic cations A and B (1lesnles9) characterized by pi- type bonds on both sides of the diamagnetic bridge X without the presence of a -type orbital (with here A=B or AneB). From a practical point of view this situation often occurs in natural and artificial magnets. In this part, we exclusively set the basic physical assumptions of the model; this will allow one to express the intermediate cationic states which are necessary for the construction of the final collective state describing the structure AXB. These last steps will be examined in part II whose final aim is the expression of exchange energies J_I vs key molecular integrals.