Solid-state NMR (SSNMR) spectra hold chemical and structural information, however the spectral peaks must be assigned to atomic sites to utilize this information. Computationally calculated chemical shifts can be assigned to experimental peaks if an accurate crystal structure is first determined. Triphenylsilanol, representative of reactive sites of important silica materials, has a challenging <sup>29</sup>Si SSNMR spectrum (Figure 1) to assign because it contains 8 chemically identical, but crystallographically unique, Si positions in the crystal resulting in 40,320 possible assignments. The size of the triphenylsilanol unit cell (Figure 2) containing 588 atoms makes quantum mechanical geometry optimizations prohibitive. We have optimized the diffraction structure using molecular mechanics with FORCITE and assigned peaks using a least-squares fit of the chemical shielding tensors calculated with CASTEP. CASTEP makes use of the Perdew-Burke-Ernzerhof generalized gradient approximation functional and a plane wave basis set. We report chemical structures and shift assignments for 1,4-dimethoxybenzene and triphenylsilanol.

Solid-state NMR chemical shift peak matching of geometry optimized organic crystals by computational methods

249th National Meeting (2015)

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