The Influence of Structure and Geometry on the Silicon-29 Chemical Shift

The bond-polarization theory is applied to 29Si chemical shifts and its dependence on the molecular geometry of SiO 2 networks. According to this theory the bond-polarization energy is linearly related to the chemical shift. This energy is calculated for various SiO 2 networks to obtain the three parameters of the correlation to the chemical shifts. The mean deviation between calculated and observed shifts is only 1 ppm. Phosphorus and silicon chemical shifts are compared especially with regard to the influence of the d pπ bond on the chemical shift. Various simplifications are discussed to give a theoretical rationalization for the empirical bond angle or bond distance formulas for the 29Si chemical shift. Furthermore the bond-polarization theory is applied to give estimates for the atomic charges on the silicon within various SiO 2 networks.