DFT analysis of cubane-type feir₃s₄ clusters. Dinitrogen binding and activation at the tetrahedral Fe site

The electronic and structural properties of the cubane-type mixed-metal sulfido clusters with a FeIr₃S₄ core and possible dinitrogen binding and activation were analyzed by density functional theory (DFT) calculations. Five different charges of the cluster and manifold of the electronic states were investigated. For each charge under consideration (+2, + 1,0, - 1, - 2) systematic analysis of structural and electronic properties was carried out. The DFT calculations show that both Fe-N and N=N bond lengths correlate with the total charge of the cluster. The length of the Fe-N bond decreased, whereas the N=N bond length increased with the number of added electrons. However, only noticeable elongation of the N=N bond was observed when the charge of the cluster became negative. Similar analysis was extended to species that have protonated dinitrogen bond. The results obtained from the DFT analysis are useful in considering the principles of the reduction of dinitrogen to ammonia at a single metal center.