Quantum Chemistry Studies On Compounds Of Silicon And Their Molecular Interactions

Compounds of silicon have been focused on for a long time. Since 1980 s, some experimental chemists had begun to synthesis and analysis silabenzene, 1,3,5-trisilabenzene and their derivatives.And theoretical chemists also made plenty of theoretical calculations of silabenzene and 1,3,5-trisilabenzene.In this thesis, silabenzene,1,3,5-trisilabenzene and the interactions of their dimer geometrys were studied by using density functional theory mainly. We optimized the geometry of silabenzene at the wB97X-d/def2-TZVPP and MP2/def2-TZVPP levels, and1,3,5-trisilabenzene geometry at the wB97X-d/def2- TZVPP level. Through the calculation of harmonic vibrational frequencies, we found that the plane silabenzene with C2 V symmetry and the plane 1,3,5-trisilabenzene with D3 h symmetry have no imaginary frequency, so they are both stable and balance configurations. We optimized some possible π… π, Si—H… π,C—H… π configurations of silabenzene dimers, and some possible π… π, Si—H… π,dihydrogen-bonds configurations of 1,3,5-trisilabenzene dimers, and then calculated the binding energies and harmonic vibrational frequencies of their dimers respectively. The results show that the silabenzene dimer whose symmetry is C1 with the binding energy-5.302kcal/mol is energetically minimum, the binding energy of Si—H… π configuration is-4.271kcal/mol, and the binding energy of C—H… π configuration is-4.174 kcal/mol. Among these1,3,5-trisilabenzene dimers, the parallel-stacked dimer with D3 d symmetry is energetically minimum, and it also has no imaginary frequency, and its binding energy is-8.528 kcal/mol.On the other hand, all the rest of 1,3,5-trisilabenzene dimers have imaginary frequencies, and they are all unstable theoretically. The SCS-SAPT0 computations in conjunction with the def2- TZVPP basis set were also performed for the silabenzene dimers and the 1,3,5-trisilabenzene dimer which are stable. It shows that, they are both largely dependent on both dispersion and electrostatic type interactions, and entrainment type is weak. However, for the former, theleading factor is dispersion type, and on the other hand, it is electrostatic type for the1,3,5-trisilabenzene dimer.