Collect. Czech. Chem. Commun. 1993, 58, 1255-1268

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


The influence of variations in the OSiO bond angle α on the anisotropy of the 29Si shielding tensor of the monosilicate anion SiO44- in C 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.