The nature of nitrogen-nitrogen bonding and the metal oxidation states within late-noble-metal pernitrides have been determined by a series of density- functional electronic-structure calculations. In contrast to alkaline-earth pernitrides such as BaN2 which contain quasi-molecular double-bonded N-2(2-) units, compounds such as PtN2 incorporate a tetravalent metal and a N-2(4-) species with a N-N single bond due to four surplus electrons within the antibonding 1 pi g* molecular orbital This fact is the source of the huge bulk moduli of PtN2 and related materials such as OsN2 and IrN2 The crystal structure of lanthanum pernitride, LaN2 reversible arrow La3+ + N-2(2-) + e(-), yet to be made, has been predicted, and its electronic structure is compared with a likewise hypothetical LaN2 which consists of both N-2(2-) and N-2(4-) pernitride units together with a trivalent lanthanum cation Finite-temperature DFT calculations predict a very moderate reaction pressure toward LaN2 starting from LaN and elemental nitrogen of less than 2 GPa at 300 K