Spin coupling in iron-containing proteins and model complexes

In the field of transition metals in biology we are concerned with a variety of homo- and hetero-polynuclear metal clusters which exhibit spin coupling. A further example for spin coupling in this field is provided by mononuclear transition metal complexes, with the paramagnetic metal site and an additional nonmetallic site forming a spin-coupled system. For both types of spin-coupled systems we present examples here, and we discuss the influence of localized and delocalized mixed-valence states, and the strength of superexchange, spin-dipolar and double-exchange contributions to spin coupling.