Manganese exchange interactions

The Mn- Mn separations in these complexes lie in the range 2.931-2.955A and the magnetic moments at room temperature observed for these complexes vary in the range 4.21. 29 /tb with the exchange interaction (/) between the manganese centers in the range — 10.6cm to — 13.2cm Cyclic voltammetry studies in methanol show two quasireversible reduction waves at about —0.3 V and —0.7 V vs. SCE. 

Monomeric species, with no exchange interaction between adjacent metal atoms, typically exhibit moments close to the spin only values. Most known compounds of manganese(II) and (III) are high spin, with the cyano compounds best known among the few low spin species. But these moments give no information about stereochemistry of the metal atom, and their purpose can be only to give information about the spin state and perhaps to help to confirm oxidation state. 

One result of this work is the conclusion that in chromia-alumina, and in other supported oxides, there must be local concentration of the supported oxide. This conclusion is reached because the Weiss constant shows definite indication of exchange interaction at concentrations of the paramagnetic ion too low to cover the surface of the support with even a monolayer. Another conclusion is that the support is sometimes able to modify the relative stabilities of oxidation states in the supported oxide. For instance, manganese oxide supported on gamma-alumina tends to be stabilized in the tripositive state, while on high-area titania it reverts to the tetrapositive state. 

Finally, a recent study reported FDMR and INS spectra of a series of hexa-nuclear manganese(III) clusters, with both 5 = 4 and 5=12 ground states (Fig. 2) [26]. Magnetically, these clusters consist of two exchange coupled triangles, and ground state spin value depends on the nature of the exchange interaction... 

Fig. 7 Representation of a complexes containing the [Mn(IV)Mn(III)303Cl] cubane core. The Mn(IV) cation is that coordinated to the three oxygen atoms of the cubane, labeled as 4 in the exchange interactions described in the text (see Eq. 10). The carbon, manganese, oxygen, chlorine, and hydrogen atoms are represented by spheres of different shades of gray, from dark to bright, respectively...

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