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

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