Interaction of Y, Y₂, Mo, and Mo₂ with NH₃. A Density Functional Study

The interaction of Y, Y₂, Mo, and Mo₂ with NH₃ is studied to understand the influence of the electronic configuration of the transition metal atoms and clusters on their reactions with ammonia. The interactions are investigated with the all-electron linear combination of Gaussian-type orbitals Kohn−Sham density functional theory (LCGTO-KS-DFT). The binding energies and harmonic frequencies characterize the equilibrium geometries. The reaction products investigated are MNH₃, MNH, M₂NH₃, M₂NH, and M₂(NH)₂. The binding energy indicates that the reaction of Y and Y₂ is possible. For Y, the stable products are YNH₃ and YNH with binding energies of 24.6 and 32.6 kcal/mol, respectively. For Y₂, the stable products of the reaction are Y₂NH₃, Y₂NH, and Y₂(NH)₂ (binding energies of 13.9, 55.5, and 110.2 kcal/mol, respectively). For Mo, the stable product is MoNH₃ with a binding energy of 8.5 kcal/mol. For MoNH, the binding energies indicate that the reactants (Mo + NH₃) are more stable than the products (MoNH + H₂) by 9.8 kcal/mol. For the Mo₂[NH₃] complex, the binding energy is 17.9 kcal/mol, in good agreement with the experimental value of 14 kcal/mol previously reported. For Mo₂, there are no other stable products of the reaction because Mo₂NH and Mo₂(NH)₂ are less stable than the reactants (Mo₂ + NH₃) by 12.7 and 10.9 kcal/mol, respectively. The differences in the bonding are explained with molecular orbital pictures. For each metal, a relationship between the electronic configurations of the transition metals and the binding energies is reported.