Out-of-plane r-aromaticity and enhanced p-aromaticity in superatom compounds-Zhi-ru Li

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 236.9 kcal/mol. Maximum nucleus-independent chemical shift (NICSmax) values of
M3
+ are located at the outside of the M3
+ ring plane about 0.6–1.5 Å for the sandwich-like structures,
which exhibit unusual out-of-plane r-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.