Infrared Spectra, Structure, and Bonding of the Group 6 and Ammonia M:NH₃, H₂N−MH, and NMH₃ Reaction Products in Solid Argon

Laser-ablated chromium, molybdenum, and tungsten atoms undergo oxidative addition reactions with ammonia during condensation in excess argon. The subject molecules were trapped in solid argon and identified by isotopic shifts and DFT frequency calculations. The 1:1 metal−ammonia complexes increased on annealing and photoisomerized to H₂N−MH and then to NMoH₃ and NWH₃, but NCrH₃ is too high in energy to be formed here. These products also increased slightly on annealing, which indicates a spontaneous reaction between group 6 metal atoms and ammonia. The NMoH₃ and NWH₃ molecules contain fully developed triple bonds with effective bond orders of 2.91 and 2.92, computed using the B3LYP density functional, and terminal metal nitride bond lengths, in agreement with those measured for larger organometallic complexes.