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 pi 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 pi MO for the most stable B2XY species is larger than that for the most stable Al2MN species. (C) 2008 Elsevier B.V. All rights reserved.