In contrast, the 2D Al TQ/MAS NMR spectra revealed a more complex nature of the prepared materials. The resonance assignments presented below were made based on the clustering (grouping) of the fitted resonances in parameter space (δF1, δiso, CQ) across all the prepared products (Figure ) and the proximity of the clusters to the values predicted by DFT calculations (CUBEs terminated by -OMe). Further refinements of the fits were made once the initial grouping was established. The full list of all the observed resonances (labelled by product number and a letter, e.g, 1/A), their Al NMR parameters and assignments are available in Table . Table and Table summarize all the model structures investigated by DFT calculations and the predicted parameters. The CQ is the most reliably fitted parameter as it depends primarily on the limits of the peak envelope, while η is the least reliable as it subtly changes the peak shape within the limits of the envelope. The fit of δiso is contaminated by the uncertainty of η. The less chemically relevant indirect chemical shift δ F1 can be measured directly with the greatest precision from the 1D projections of the Al TQ/MAS spectra. Therefore, the assignments were made using plots of δiso/CQ (Figure ) and δF1/CQ (Figure ), with the latter showing more distinct clustering and serving as the starting point for the assignment. Figure shows the lack of significant clustering in the η/C Q space, demonstrating the unreliability of the fitted η values.