Structures and aromaticity of the planar B₂XY (X = N, P and Y = O, S, Se) and Al₂MN (M = C, Si, Ge and N = S, Se) clusters

Clusters B₂XY (X = N, P and Y = O, S, Se) and Al₂MN (M = C, Si, Ge and N = S, Se) species are theoretically investigated with density functional theory (DFT) method. The results show that although the most stable isomers for B₂XY and Al₂MN species have a similar structure, they show a different symmetry at the B3LYP/6-311+G* level. NICS analysis displays that both B₂XY and Al₂MN possess strongly aromatic character, and the atomic size has an important effect on the stability of stable planar structures for these species. In addition, the presence of two delocalized π electrons does agree well with the (4n + 2) Huckel rule, which confirms that aromaticity plays an important role in the stability of planar structures for B₂XY and Al₂MN species. Moreover, MO analysis shows that the delocalized extent of π MO for the most stable B₂XY species is larger than that for the most stable Al₂MN species.