125Te and 57Fe nuclear resonance vibrational spectroscopic characterization of intermediate spin state mixed-valent dimers

While most biological and biomimetic mixed-valent [2Fe-2S]+ clusters exhibit a S = 1/2 ground spin state, substitutions with Se and Te significantly perturb the electronic structure and yield clear S = 3/2 spin state signatures. Here, the authors probe the vibrational dynamics of the Fe and Te centers using 57Fe and 125Te nuclear resonance vibrational spectroscopy and DFT calculations.