A COMPUTATIONAL STUDY OF METAL-DINITROGEN COORDINATION

Local density functional theory (DFT) discrete variational Xalpha (DVXalpha) 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 DVXalpha 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.