Correlating geminal 2JSi-O-Si couplings to structure in framework silicates.

The dependence of a 29Si geminal J coupling across the inter-tetrahedral linkage on local structure was examined using first-principles DFT calculations. The two main influences on 2JSi-O-Si were found to be a primary dependence on the linkage Si-O-Si angle and a secondary dependence on mean Si-O-Si linkage of the two coupled 29Si nuclei. An analytical expression describing these dependences was proposed and used to develop an approach for relating the correlated pair of 2JSi-O-Si coupling and mean 29Si isotropic chemical shift to the linkage Si-O-Si angle and the mean Si-O-Si angle of the two coupled 29Si nuclei. An example of this analysis is given using 29Si NMR results from the siliceous zeolite Sigma-2.