All samples were analyzed by ICP-OES for Al, Sn, and P (samples with TEPO) content in order to provide independent validation of the information obtained from gravimetric methods (degree of condensation, composition, initial stoichiometry). The precisely weighed sample (~60 mg) was digested by 2 cm 3 of a 1:1 mixture of 65% HNO3 and 50% HF and diluted to 100.00 cm . The volumetric solutions were measured on the Thermo Scientific iCAP Table . Slices through the Al TQ/MAS NMR spectrum of product 5 and the corresponding line shape simulation fits. Table . Slices through the Al TQ/MAS NMR spectrum of product 6 and the corresponding line shape simulation fits. Table . Slices through the Al TQ/MAS NMR spectrum of product 7 and the corresponding line shape simulation fits. Table . Slices through the Al TQ/MAS NMR spectrum of product 8 and the corresponding line shape simulation fits. Composition: ICP-OES: 0.823 wt% Al, 46.9 wt% Sn; Gravimetry: 0.820 wt% Al, 45.9 wt% Sn. Table . Slices through the Al TQ/MAS NMR spectrum of product 12 and the corresponding line shape simulation fits. Table . Slices through the Al TQ/MAS NMR spectrum of product 13 and the corresponding line shape simulation fits. Table . Slices through the Al TQ/MAS NMR spectrum of product 14 and the corresponding line shape simulation fits. Table . Slices through the Al TQ/MAS NMR spectrum of product 15 and the corresponding line shape simulation fits.