Looking into the future, the next logical step towards understanding the electronic structure of 1 and 2 would be to combine the global fit of computational results with experimental XAS data. In the past, combining Density Functional Theory (DFT) with experimental data was groundbreaking and the only way to give chemical meaning to the experimental data. Verification via XES showed that the central atom in FeMoco and FeVco's iron-sulfur is carbon. Due to this unusual octahedral-coordinated central atom, computational model complexes have become more complicated by using the Density Matrix Renormalization Group (DMRG) method with an extended active space of up to 113 electrons in 76 orbitals. This gives further evidence of open-shell character and their low-energy states in highly covalent active sites like the FeMoco active site of nitrogenase.