Collect. Czech. Chem. Commun. 1993, 58, 1255-1268
https://doi.org/10.1135/cccc19931255

Contribution to the Semiempirical Interpretation of the Anisotropy of the 29Si NMR Shielding Tensor in Silicates. II. Influence of Changes in the O-Si-O Bond Angle in SiO44- Ion

Christine Vogel, Renate Wolff and Reiner Radeglia

Central Institute of the Physical Chemistry, Analytical Centre, Rudower Chaussee 5, Berlin-Adlershof, D O-1199, Germany

This article is part of serial Contribution to the Semiempirical Interpretation of the Anisotropy of the 29Si NMR Shielding Tensor in Silicates.

Abstract

The influence of variations in the OSiO bond angle α on the anisotropy of the 29Si shielding tensor of the monosilicate anion SiO44- in C3ν symmetry has been investigated by semiempirical CNDO/2 calculations. In the valence basis set of the silicon atom, no d-orbitals were employed. It could be shown that the terms characterizing the four Si-O bond contributions to ∆σ are of greatest importance for reproducing the experimentally observed trend of anisotropy signs in silicates. Both the increasing O(1)-Si-O(B) bond angle α, and the decreasing Si-O(1) bond length r(Si-O(1)) (and vice versa) exhibit an amplifying geometrical influence on ∆σ.