Ab Initio Study on the Aromaticity of All-Metallic Anion $La^{2-}_4$

Abstract

We extended the aromaticity concept to all-metallic anion $La^{2-}_4$ and then performed Ab intio calculations (B3LYP/LANL2DZ, B3PW91/LANL2DZ andMP2/LANL2DZ) on the selected structures. The computed results indicate that anion $La^{2-}_4$ has two stable isomers: one is the bidentate $C_{2v}$ structure and another is the square planar $D_{4h}$ structure. The further analysis on energies shows that the square planar $D_{4h}$ structure is more stable than the bidentate $C_{2v}$ structure. The computed nucleus-independent chemical shifts (NICS) on the most stable $D_{4h}$ structure show that the square planar $La^{2-}_4$ ring exhibits higher degree of aromaticity. The detailed MOs analysis further reveals that the square planar $La^{2-}_4$ ring possesses four independent delocalized bonding systems, each has two electrons satisfying the $4n + 2$ electron counting rule of aromaticity, suggesting that these species have four-fold aromaticity.