Laser-ablated Y and La atoms react with nitrogen to produce metal nitrides and dinitrogen complexes, whereas thermally evaporated Y and La atoms form only dinitrogen complexes. The ligated mononitride complexes (NN)(x)YN and (NN)(x)LaN at 771.6 and 761.7 cm(-1) in solid nitrogen are identified from nitrogen-15 shifts. These complexes predict gas-phase fundamentals near 800 and 790 cm(-1) respectively for YN and LaN. The (YN)(2) and (LaN)(2) molecules and dinitrogen complexes are also identified from nitrogen-15 shifts and result from the reaction of two metal atoms with a single dinitrogen molecule involving the Y(N-2) and La(N-2) intermediate species. The same saturated (YN)(2)(NN)(x) and (LaN)(2)(NN)(x) dinitrogen complexes are prepared on annealing solid argon containing 2% N-2 and deposition in pure nitrogen. The growth of ligated (YN)(2)(NN)(x) and (LaN)(2)(NN)(x) on annealing suggests that this nitrogen fixation reaction involves little activation energy.