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

Abstract

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 ²J_Si–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 ²J_Si–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.