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.