Example 1 NIS Studies of an Fe III -azide Cyclam-acetato Complex

2 Example 1 NIS Studies of an Fe(III)-azide(Cyclam-acetato) Complex 

The Fe(III)-azide(cyclam-acetato) complex, as seen earlier, serves as a precursor for generation of the superoxidized Fe(V)-nitrido(cyclam-acetato) complex by means of photolysis with 420 nm light [63, 108] (Fig. 5). 

The Fe(lll)-azide-precursor and the photolysed product were characterized by NIS spectroscopy coupled to detailed DFT calculations [63]. The result of the study provides additional evidence in favor of a low-spin 5=1/2 ground state of the Fe(V)-nitrido complex. Here we show how first-principles calculations assist in quantitative analysis of experimental NIS data for the Fe(lll)-azide complex. 

The fitted and calculated vibrational frequencies and normal mode composition factors corresponding to the 17 most important NIS bands are presented in Table 5.9. It is evident that the vibrational peaks in the calculated NIS spectrum are typically 0-30 cm lower than to the experimental values. In the calculated NIS spectra, there are two small peaks at 635 and 716 cm (Fig. 5.14b) that are not visible in the experimental spectrum. According to the normal mode calculations these are Fe-N-N and Fe-O-C deformation vibrations. Small admixtures of Fe-N and Fe-O stretching modes account for the calculated nonzero normal mode composition factors. Although the calculated relative intensities are slightly above detection limit dictated by the signal-to-noise ratio, they are determined by values of pea which are very small (0.028 and 0.026 for the peaks at 635 and 716 cm ). They must be considered to be within the uncertainties of the theoretical 

The normal-mode analysis has shown that there are 17 vibrational modes that are characterized by significant involvement of the Fe nucleus (i.e. large values of Fea)- frequencies and normal mode composition factors corresponding to these vibrations are described in Table 5.9. 

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