Atomic and Electronic Structure of Organosilicon Polymers of Acetylene Derivatives: X-ray Spectral and Theoretical Study

The atomic and electronic structures of two organosilicon polymers [–Ph₂Si–(C≡C)₂–]_n (P1) and [–Ph₂Si–(C≡C–C≡C)₂–]_m (P2) (where Ph is a phenyl group) of acetylene and diacetylene types are studied using the methods of density functional theory and X-ray emission spectroscopy. The SiK_β1 X-ray emission spectra of these polymers are interpreted on the basis of analysis of the distribution of partial electronic states obtained from quantum chemical calculations. The quantitative characteristics of the parameters of the chemical interaction of atoms, such as population, natural charges, and electronic configurations in the studied polymers, are obtained on the basis of analysis of hybrid natural bond orbitals. The values of the polarization coefficients of natural bond orbitals indicate the localization of electron density predominantly on carbon atoms. The electronic configurations for carbon atoms in different fragments differ significantly. For the C atoms of ethynyl (diethynyl) fragments, they are close to the linear σ bond of the sp^1.03 (P1) and sp^0.95 (P2) type, while for the C atoms of phenyl fragments, they are sp^2.42, which are intermediate between sp² and sp³, in accordance with molecular geometry. The natural charges on Si in both polymers are almost the same: +1.58e, +1.59e (e is the elementary charge), while the natural charges for carbon atoms of the diethynyl group decrease in comparison with the charge for the carbon atom of the ethynyl group from –0.42e to –0.36e.