Structure and aromaticity of Bi5-, Bi5M (MÂ =Â Li, Na, K) and Bi5M+ (MÂ =Â Be, Mg, Ca) clusters

The equilibrium geometries, electronic structures, harmonic vibrational frequencies, and nucleus independent chemical shifts (NICS) of Bi5-, Bi5M (M = Li, Na, K), and Bi5M+ (M = Be, Mg, Ca) clusters are calculated by the density functional theory (DFT) method. Our calculation show that the ground states of Bi5-, Bi5M, and Bi5M+ species are predicted to be the D5h, C5v, and C5v structures, respectively. In addition, the Bi5- unit preserves its structural and electronic integrity in forming the Bi5M and Bi5M+ complexes. Molecular orbital analysis and NICS show that the planar Bi5- (D5h) anion satisfies the Hükcel rule of 4n + 2 π electrons and magnetic criteria for aromaticity with six delocalized π electrons and negative NICS values. The dissected NICS suggests that the aromaticity of Bi5- (D5h) arise primarily from the contributions of Bi-Bi σ bonds and Bi-Bi π bonds, while the aromaticity of Bi5M and Bi5M+ mainly owe to the Bi-Bi σ bonds.