A computational study of metal–dinitrogen co-ordination

Abstract

Local density functional theory (DFT) discrete variational X_α(DVX_α) calculations have been performed on the model metal–dinitrogen system trans-[MA₄(N₂)₂](M = Mo, A = PH₃ or SH₂; M = W, A = PH₃) and trans-[MClA₄(N₂)](M = Mo, A = PH₃ or SH₂). Molecular-orbital and charge density analyses demonstrate a reasonable qualitative correlation between theory and experiment with respect to metal–ligand bonding, N–N stretching frequencies, and the sites and relative rates of attack on co-ordinated N₂ by protons and organic radicals. Comparisons with ab initio Hartree–Fock theory results for [Mo(PH₃)(N₂)₂] show that the DVX_α method gives a better description of the charge distribution. Attempts to quantify the theoretical predictions via binding-energy calculations have been less successful. Evidently, a more sophisticated DFT treatment will be required for improved quantitative accuracy.