Structures and aromaticity of the C2N2− anion, M(C2N2) (M = Li, Na, K) and [N(C2N2)]+ (N = Be, Mg, Ca) clusters

Geometrical structure, aromaticity and other properties of C2N2−, M(C2N2) (M = Li, Na, K) and [N(C2N2)]+ (N = Be, Mg, Ca) species are theoretically investigated with density functional theory (DFT) methods. Calculation results show that for C2N2− species, the planar structure with D2h symmetry is the global minimum at the B3LYP/6-311+G* level. Natural bond orbital (NBO) analysis indicates the existence of delocalization in the most stable C2N2− species and its planar complexes. Nucleus-independent chemical shift (NICS) and molecular orbital (MO) analysis further reveal that that planar M(C2N2) and [N(C2N2)]+ species preserve the aromatic nature of the most stable C2N2− unit.