Out-of-plane σ-aromaticity and enhanced π-aromaticity in superatom compounds Li3 +N4 2−M3 + (M=Li, Na and K)

Abstract: The structures of sandwich-like and chain-like superatom compounds Li3–N4–M3 (M=Li, Na and K) are obtained at the MP2/6-311+G(2d) level. These structures are stable own to large interaction energy ranging from −184.4 to −236.9kcal/mol. Maximum nucleus-independent chemical shift (NICSmax) values of M3 + are located at the outside of the M3 + ring plane about 0.6–1.5Å for the sandwich-like structures, which exhibit unusual out-of-plane σ-aromaticity. The NICSmax values of N4 2− in the sandwich-like structures are obviously larger than that of corresponding chain-like structures, which show that the two adjacent rings (Li3 + and M3 +) enhance the aromaticity of N4 2− ring in the sandwich-like structures. In addition, the N4 in the superatom compound is proposed as a new “supersulfur” atom. [Copyright &y& Elsevier]