Conformational and spin state interconversions in transition metal complexes

Iron(u), cobalt(ii) and nickel(ii) sixand five-coordinated complexes are reviewed, with particular attention to the factors influencing the spin multiplicity of the ground state. In the case of octahedral complexes, the Dq parameter and the effects of distortion are considered sufficient to interpret the experimental data, whereas in the case of five-coordinated complexes a new parameter, the overall nucleophilic reactivity constant n° is introduced in order to account for the spin state of the complexes. In this latter case a detailed discussion of the influence of the geometry on the spin state is presented. The methods for rationalizing the magnetic behaviour of complexes showing spin state equilibria are critically discussed.