Low and high spin forms

The marked changes in spectra accompanying changes in spin state may be used as a simple method for estimating spin state populations. When attempting to relate this property to optical spectra or to the chemical behaviour of haemoproteins it is important to realise that spin state transitions may be temperature dependent. An example of this is catalase compound II at 77°K it is a mixture of low and high spin forms, at 20°K it is predominately high spin, whilst at room temperature optical spectra show it to be mainly low spin [11]. 

Figure 2 In a d metal ion, both low- and high-spin complexes are possible, depending on the value of A. A high A leads to the low-spin form...

Structural information about simple Ni(iii) compounds is limited to those containing F or 0. KsNiFg has been assigned the KsFeFg structure and has a moment of 2-5 BM, intermediate between the values for low- and high-spin. It contains octahedrally coordinated Ni(iii). Oxides LnNiOs formed with the 4f elenients have the perovskite structure, while NiCrOs has a statistical corundum structure it is concluded from the magnetic properties that this compound contains high-spin Ni(iii). ... 

---