Ab initio study of the topology of the charge distribution of H3SiO(H)AlH3 conformers

The topologic properties of the electronic charge distribution of conformers of H₃SiO(H)AlH₃ molecule hydroxyl groups of zeolites are reported. The studied properties—total density, Laplacian density, and bond ellipticity—were evaluated at the position of the critical points of the O? Si, O? Al, and O? H bonds, by using Hartree–Fock and second‐order Møller–Plesset levels of theory, and the STO/6‐31+G(d,p) standard basis set. For the H₃SiO(H)AlH₃ molecule, four conformers are identified. It is demonstrated that for these conformers, the total density and Laplacian density remain almost constant by effect of the rotations of the T? H bonds, T=(Si, Al), around the corresponding O? T bonds, respectively. However, these rotations induce sensible variations in the ellipticity at the position of the critical point of the O? Al bonds, which are reflected in the OH bond distance, OH vibrational mode, and the stabilization energy of conformers. These results lead to a linear relationship between the magnitude of the bond ellipticity at the critical point of the O? Al bonds and the frequency values of the OH bonds, with a correlation coefficient of r²=0.98. In addition, a good linear relationship between the ellipticity of the O? Al bond and the pattern of the stabilization energy of conformers was also found. © 1999 John Wiley & Sons, Inc. Int J Quant Chem 76: 1–9, 2000