1,2,3-Dithiazolyl and 1,2,35-Dithiadiazolyl Radicals as Spin-Bearing ...

is quite similar to the spin-polarization discussed earlier. This will result in
antiferromagnetic coupling if the two metal orbitals in question are the same as is
illustrated in Figure 1-13 although depends on the bonding motif of the molecular system
being investigated.
Ferromagnetic coupling provides systems which have a non-zero spin ground state
and are therefore of interest in the field of molecular magnetism, however if two metal
ions couple antiferromagnetically to one another it will give rise to a spin state of zero.
Some work, however has investigated what are known as spin-frustrated systems which
involve, for example, three manganese centers 119,120 or more such as in clusters 121 or
Figure 1-13. Orbital cartoon illustrating the
mechanism of superexchange. For two generic metal
centers M and a closed-shell bridging ligand L.
Figure 1-14. Spin frustration for a triangular
system of three spin centers.
chains. 122 If we consider two antiferromagnetically coupled manganese ions Mn1 and
Mn2 with a coupling constant J Mn1-Mn2 , and then include a third Mn3 which is equidistant
from each of the first two such that the coupling constant |J Mn3-Mn2 |= |J Mn3-Mn1 | = |J Mn2-Mn1 |,
then the tendency would be for the third ion to couple antiferromagnetically such that
each of the values are negative. This is illustrated in Figure 1-14 and describes an
impossible situation. 123,124 As this circumvents the natural tendency of these ions, they are
anthropomorphized as being frustrated.
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