[N3MN5]q: a type of low-lying sandwich-like isomer on [N8M]q hypersurface with (M, q) = (Ni, 0), (Co, -1), and (Fe, -2).

Recently, design and assembly of small, high-energy-density, all-nitrogen units into more complex sandwich-like forms have received growing attention. In this paper, we report a type of heterodecked sandwich-like structures [N(3)MN(5)](q) containing two odd-membered all-nitrogen rings (N(3) and N(5)) on the hypersurface of [N(8)M](q) [(M, q) = (Ni, 0), (Co, -1), (Fe, -2)]. At the B3LYP/6-311+G(d) level, the new isomers are energetically more stable than the previously reported homodecked sandwich-like isomers [N(4)MN(4)](q) based on the even-membered all-nitrogen ring N(4)(2-). In particular, the eta(3)-eta(2) (eta(3)-eta(1)) isomers of [N(3)MN(5)](q) [(M, q) = (Ni, 0), (Co, -1), (Fe, -2)] possess considerable kinetic stability for laboratory characterization. The bond length and natural charge analysis of [N(3)MN(5)](q) [(M, q) = (Ni, 0), (Co, -1), (Fe, -2)] indicate that each complex possesses the smallest triplet all-nitrogen ring (3)N(3)(-). The unique stability of the presently designed heterodecked sandwich-like complexes await future laboratory investigations.