Estimations of Fe0/−1–N2 interaction energies of iron(0)-dicarbene and its reduced analogue by EDA-NOCV analyses: crucial steps in dinitrogen activation under mild conditions

Benchmark Study of Density Functional Theory Methods in Geometry Optimization of Transition Metal-Dinitrogen Complexes

The current benchmark study is focused on determining the most precise theoretical method for optimizing the geometry of transition metal-dinitrogen complexes. To accomplish this goal, seven density functional (DF) methods from five distinct classes of density functional theory (DFT) have been selected, including B3LYP-D3(BJ), BP86-D3(BJ), PBE0-D3(BJ), ωB97X-D, M06, M06-L, and TPSSh-D3(BJ). These DFs will be utilized with the Karlsruhe basis set (def2-SVP). To carry out this benchmark study, a total of forty-two structurally diverse transition metal-dinitrogen compounds with experimentally known X-ray data have been selected from the Cambridge Crystallographic Data Centre (CCDC). Based on a comparison of the theoretical data with experimental values (X-ray) of the selected transition metal-dinitrogen compounds, statistical parameters such as root-mean-square deviation (RMSD) and N-N and M-N bond lengths are obtained to evaluate the performance of the seven chosen DFs. According to the obtained results, among all DFT methods used in the study, Minnesota functionals (M06 and M06-L) and TPSSh-D3(BJ) show good performance, with lower RMSD values. This suggests that these three methods are the most reliable for optimizing the geometry of transition metal-dinitrogen complexes. Based on the absolute errors of the N-N and M-N bond lengths relative to the X-ray data, further analysis is conducted, and it is determined that M06-L is the best functional for optimizing the geometry of transition metal-dinitrogen compounds. Additionally, the influence of using a high-level basis set (def2-TZVP) compared to def2-SVP on the calculated RMSD among the seven chosen methods is found to be negligible.

Dinitrogen Binding and Activation: Bonding Analyses of Stable V(III/I)-N2-V(III/I) Complexes by the EDA-NOCV Method from the Perspective of Vanadium Nitrogenase

The FeVco cofactor of nitrogenase (VFe₇S₈(CO₃)C) is an alternative in the molybdenum (Mo)-deficient free soil living azotobacter vinelandii. The rate of N₂ reduction to NH₃ by FeVco is a few times higher than that by FeMoco (MoFe₇S₉C) at low temperature. It provides a N source in the form of ammonium ions to the soil. This biochemical NH₃ synthesis is an alternative to the industrial energy-demanding production of NH₃ by the Haber-Bosch process. The role of vanadium has not been clearly understood yet, which has led chemists to come up with several stable V-N₂ complexes which have been isolated and characterized in the laboratory over the past three decades. Herein, we report the EDA-NOCV analyses of dinitrogen-bonded stable complexes V(III/I)-N₂ (1-4) to provide deeper insights into the fundamental bonding aspects of V-N₂ bond, showing the interacting orbitals and corresponding pairwise orbital interaction energies (ΔE _orb(n)). The computed intrinsic interaction energy (ΔE _int) of V-N₂-V bonds is significantly higher than those of the previously reported Fe-N₂-Fe bonds. Covalent interaction energy (ΔE _orb) is more than double the electrostatic interaction energy (ΔE _elstat) of V-N₂-V bonds. ΔE _int values of V-N₂-V bonds are in the range of -172 to -204 kcal/mol. The V → N₂ ← V π-backdonation is four times stronger than V ← N₂ → V σ-donation. V-N₂ bonds are much more covalent in nature than Fe-N₂ bonds.