Magnetic coupling systems

In the case of magnetically coupled systems. Curie relaxation is simply additive as long as the magnetic susceptibility is the sum of the two components. When the magnetic susceptibility is not a simple sum of the components, the magnetic susceptibility contribution of each metal ion should be evaluated. 

There are no treatments for the pseudocontact term, since the orbital part has never been considered when dealing with magnetic coupled systems. However, Eqs. (6.7) and (6.10) hold for the hyperfine splitting in EPR spectra of both solids and solutions [1]. Therefore the same reasoning is likely to apply to the pseudocontact shift as well. The major complication arises from the point-dipolar nature of the pseudocontact shift treatment, which contrasts with the idea of a polymetallic center. 

A species of this type is probably best described as a [Fe - NO ] complex, with a resultant spin S = 3/2 characteristic of a shongly magnetically coupled complex. Magnetically coupled systems exhibiting the combined influence of and an electrostatic interaction termed Heisenberg exchange are discussed in Section 4.5. 

Fig. 5. Temperature dependence of the isotropic shift values calculated in a Fe(II)-Fe(III) magnetic coupled system, with a J coupling constant of 100 cm" (see text) b) Calculated dependence of the isotropic shift values in a Fe(II)-Fe(III) magnetic coupled system, and their ratio broken line) as a function of the J value. Temperature is 303 K...

We would like to stress that any analysis should start using the correct equations derived for the magnetically coupled system. This treatment is quite general and can be applied to both homo- and heterodimers. In the former class we can mention p-oxo diiron (III) porphyrins [4] and dinuclear copper(II) complexes... 

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