Antiferromagnetic metals coupled state

There are three reasonable combinations of metal oxidation states for oxidized Type 3 copper that are consistent with spectral and redox data (1) Cu(I) Cu(I) with some other group, e.g., disulfide, functioning as a two-electron acceptor (2) Cu(I)-Cu(III) where Cu(III) is low spin and (3) an antiferromagnetically coupled Cu(II)-Cu(II) dimer. Magnetic susceptibility studies on Rhus vernicifera laccase have established that the two Type 3 copper atoms in this enzyme are present as an antiferromagnetically coupled Cu(II) dimer (4). The Type 3 copper atoms of hemocyanin and tyrosinase appear to be similarly coupled and separated by 3-5 A (5,6,7). Further structural information on the Type 3 copper chromophore is scanty neither the identity of the ligands nor the geometry of the site has been ascertained. There is likewise a paucity of literature on binuclear copper complexes that exhibit structural features expected for Type 3 copper. 

As it was already mentioned, the ordered double perovskite St2FeRe06 is also predicted to have a half-metallic ground state. The observed Ms of 2.7 pB/f-u. at 4.2 K is smaller than expected (3 pB/f-u.) for an antiferromagnetic coupling between Fe (d ) and Subsequent to the... 

A more general point is that the maximum spin is often not attained due to antiferromagnetic coupling. In Gd(III) systems, Msat can usually be attained in moderate fields, whereas when transition metals are involved the spin state can be less than the maximum possible. Here, Gd(III)4Cu(II)8 has a spin of S = 18, the maximum possible (albeit field induced). 

When I J is of the order of hundreds of wavenumbers, i.e., it is of the order of kT, then the excited S levels are not fully populated. In homodimers antiferromagnetically coupled, the ground state is diamagnetic (S = 0). If only one metal ion is sensed by the resonating nucleus, nuclear relaxation... 

In practice, however, already with a comparatively small number of metal atoms it is no longer feasible to investigate all possible spin states with all potential realizations by various local spin distributions. Assumptions on the interaction of the metal centers on the basis of their structural arrangement and experimental susceptibility measurements have to be made. For example, for the BS state of a tetranuclear transition-metal cluster, one has to decide which of the four metal atoms couple in an antiferromagnetic fashion with each other. Prominent coupling schemes are, e.g., the dimer-of-dimers 2-plus-2-type or the 3-plus-... 

---