Redox-active centers spectroscopic features

The above theoretical studies based on structural models, and their possible involvement in H2 activation or production, give some insight into the possible redox levels of the active site. However, they focus only on the active center. They do not consider at all the protein environment which is crucial to the reactions that this site promotes, i.e., the availability of energetically favorable pathways for proton and electron transfer in and out of this active site. Nevertheless, these theoretical calculations have reproduced some of the spectroscopic features (i.e., stretching frequencies) of synthetic models, which lends confidence to the reliability of the computations. A reasonable agreement in all these calculations is that H2 binds to an Fe center and not Fe, which is consistent with the experimental fact that the mixed-valent active form of the enzyme has at least one Fe in the +2 oxidation state. This is also in agreement with the formation of stable 7 -H2 complexes of d metals. 

The redox-active metalloligand [Ru(Cp) N=C-C(pz)3 ][PF6] reacts with [Ir(COD)Cl]2 giving a bimetaUic Ru -Ir complex [Ru(Cp) i-N=C-C(pz)3 Ir(COD)Cl2] [PFe] upon activation of the C=N moiety. This heterobimetaUic complex features an unprecedented metallacyclic alkyl-amido carbene core structure coordinated to an Ir center. A DFT study on structures, spin states, FMOs, and UV-VIS spectroscopic properties of [M(Tp)(CvH5N)(PPh3)(N3)] (M= Ru or Fe) has been carried out in order to understand whether Ru can be replaced by cheaper Fe in photosensitizers for DSSCs. ... 

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