Solution state structure determination of silicate oligomers by 29Si NMR spectroscopy and molecular modeling

Evidence for nine new solution state silicate oligomers has been discovered by Si-29 NMR homonuclear correlation experiments of Si-29-enriched samples. In addition to enhancing signal sensitivity, the isotopic enrichment increases the probability of the Si-29-Si-29 two-bond scalar couplings that are necessary for the observation of internuclear correlations in 2-D experiments. The proposed assignments are validated by comparisons of experimental and simulated cross-peaks obtained with high digital resolution. The internuclear connectivity indicated by the NMR data suggests that several of these oligomers can have multiple stereoisomers, including conformers and/or diastereomers. The stabilities of these oligomers and their possible stereoisomers have been investigated by electronic structure calculations.