Contribution of the fine structure terms to thegvalues of the biological Fe <scp>iii</scp>–Fe <scp>ii</scp>clusters

The states of the different spin multiplets which result from the antiferromagnetic interaction in the Fe iii–Fe ii pairs are mixed by the fine structure Hamiltonians relative to each iron atom. The contribution of this effect to the g values of the lowest Kramers doublet is discussed for 2Fe clusters present in different groups of metalloproteins. Special attention is given to iron–sulfur proteins and hemerythrins where models have been developed to discuss the structural implications of the magnetic properties.