Compounds of nitrogen with a more electropositive element. Boron nitride is a covalent compound having macromolecular crystals. Certain electropositive elements, such as lithium, magnesium, and calcium, react directly with nitrogen to form ionic nitrides containing the N 3− ion. Transition elements form a range of interstitial nitrides (e.g. Mn4N, W2N), which can be produced by heating the metal in ammonia.