Ab initio studies on the aromaticity of bimetallic anionic clusters XGa3- (X = Si, Ge)

The structures and vibrational frequencies of bimetallic anionic clusters XGa3-(X = Si, Ge) and neutral clusters MXGa3(X = Si, Ge, M = Li, Na, K, Cu) have been studied by four ab initio methods, B3LYP, B3PW91, PW91PW91, MP2 and 6-311 + G(3df) basis sets. Three stable structures with C-2V, C-3V, C-S symmetry, respectively, for each of XGa3- and three stable structures with the same C-S symmetry for each of MXGa3 have been found. The analyses on the structures, vibrational frequencies, molecular orbitals indicate that the heterocyclic planar isomers with C-2V symmetry are the global minimum for the XGa3- species and exhibit the characteristics of aromaticity according to the current accepted criterion for aromaticity. The comparison of the structures, vibrational modes and frequencies between the isolated planar XGa3- isomers and the XGa3- units in the MXGa3 complexes shows that the heterocyclic planar isomer of each XGa3- species preserve the features of its structure and vibrational modes in forming the MXGa3 complexes. (C) 2004 Elsevier B.V. All rights reserved.