η⁵-N₅^--metal-η⁷- N₇^3-: A new class of compounds

Ab initio calculations at the B3LYP and MP2 levels suggest that a series of compounds with the general formula N₅MN₇ (M = Ti, Zr, Hf, Th) are locally stable. These compounds are thermodynamically at least as stable as the recently suggested ScN₇ molecule. N₅ThN₇ seems the most stable of all. It lies 21.5 kcal/mol below a transition state, corresponding to the opening of one N-N bond in the N₇ ring, and only 132 kcal/mol above Th + 6 N₂, or 22 kcal/(mol N₂).