A QUANTUM CHEMICAL STUDY OF SILSESQUIOXANES: H8Si8O12, Me8Si8O12, H@Me8Si8O12, He@Me8Si8O12+, AND He@Me8Si8O12
S. G. Semenov, M. E. Bedrina
Keywords: silsesquioxanes, endocomplexes, helium, cubic symmetry, structure, polarizability, PBE0, B3LYP, cc-pVTZ, MP2
Abstract
Quantum chemical PBE0 and B3LYP/cc-pVTZ, PBE0, B3LYP, RHF and MP2/6-31G(d,p) methods are employed to calculate the structural parameters of octa(silsesquioxane) H8Si8O12 and octa(methylsilsesquioxane) Me8Si8O12. These molecules and complexes Н@Me8Si8O12, Не@Me8Si8O, and Не@Me8Si8O12 have highly symmetric (Oh) equilibrium configurations. With the use of the PBE0 method and a cc-pVTZ multicenter basis set common for the complex and its components coincidence is achieved between the calculated polarizability of a free He atom and the experimental value of 0.21 Å3 and the polarizability depression of 0.17 Å3 was found for Нe@Me8Si8O12. In order to avoid the false conclusion about molecular symmetry the calculations of the structure of silsesquioxanes must be performed with sufficiently high accuracy (Int = ultrafine and Opt = tight in the use of the GAUSSIAN program).
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