The species NiN2, CrN2, and PtN2 have been identified by i.r. spectroscopy in low-temperature matrices. The i.r. spectra of dinitrogen chemisorbed on metal clusters of copper, chromium, and nickel have also been obtained, the former for the first time. The bands due to NiN2 and CrN2 are split in the nitrogen matrix due to the presence of different sites. It is suggested that the reason for the lack of observation of dinitrogen complexes beyond the bis-adduct is the deficiency of charge on the metal when dinitrogen binds as a ligand in an imperfectly synergistic process.