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F.E. Mabbs and D.J. Machin, Magnetism and Transition Metal Complexes, Dover Publications, Inc. Mineola, NewYork (Amazon)

Chapter 7: The magnetic properties of polynuclear transition metal complexes

Difference between "intermolecular antiferromagets" (3 D systems) and intramolecular AFM. For the latter the maximum in the susceptibility is much broader.
Explanation of direc exchange and superexchange. Example: copper(II), Mn2(CO)10, M-O-M.
Two approaches to explain magnetic susceptibilities of polynuclear transition metal complexes: orbital theory and dipolar coupling approach of Van Vleck. They mostly describe the dipolar approach.
"Dipolar coupling", the same cos dependence as potential energy between two dipoles. That is where the name comes from. Magnetic excange between nearest neighbours may be represented in a spin Hamiltonian for the system by a term:
H = -2\, \sum_{neighbours} J_{ij}\cdot \hat{S}_i\cdot \hat{S}_j
where J_{ij} is an exchange integral between centres i and j.

Functions for \chi(T) were derived for binuclear complexes for S_i = S_j = 1/2 (Cu(II)), S_i=S_j = 3/2 (Cr(III), Co(II)- no example), S_i=S_j = 5/2 (Fe(III)), trinuclear complexes