“…For example, the N 6 ring is reported in MN 3 (M = Li, Na, K, Rb, Cs, Mg, Ca) 18–24 and MN 6 (M = Ba, W) 25,26 compounds. The N 5 ring is found in MN 5 (M = Li, Na, K, Rb, Cs, Ca, Sr, Ba, Cu, Ag), 22,24,25,27–33 MN 10 (M = Be, Mg, Ba, Zn) 25,34,35 and MN 15 (M = Al, Ga, Sc, Y) 36,37 compounds. The armchair N-chain is found in MN 4 (M = Be, Mg, Ca, Sr, Ba, Fe, Zn, Re, Ge), 23–25,31,38–42 MN 6 (M = Fe, Ca), 24,39 MN 8 (M = Fe) 39 and MN 10 (M = Hf) 43 compounds.…”