Compounds containing the dinitrogen molecule, N₂, bound to a metal (also called dinitrogen complexes). While it was long known that molecular nitrogen avidly binds to the surface atoms of many metallic phases, no reaction of molecular nitrogen has been observed under the conditions of ordinary solution chemistry. Indeed, chemists had been so accustomed to regard nitrogen as a completely inert gas at ordinary temperatures that the formation of coordination compounds with molecular nitrogen aroused general surprise when first reported in the mid-1960s. Since then the interaction of molecular nitrogen with coordination compounds has been the subject of intensive research. Today the capability of molecular nitrogen to enter into coordination compounds as a ligand is established beyond any doubt, and it is at least partly understood under which conditions the dinitrogen molecule can lose its customary inertness.