The mass lost as the volatile byproducts was used to calculate the gravimetric degree of condensation (DCG / %) of the reacting functional groups DCG(SnMe3) and DC G (AlX), defining the average connectivity at the CUBE and Al, respectively. Ideally, only a single byproduct would be generated (SnMe 4 , SnMe 3 Et, or SnMe 3 Cl), however additional SnMe4 was observed in conjunction with each of the expected byproducts. The excess of SnMe 4 will be further linked to an unexpected formation of [AlO 4 ] -species and therefore it is conveniently quantified in mol% with respect to the Al content as DCG(SnMe4). In the case of compounds L-AlCl3, L-AlEt3, and [Me4N] [AlCl4], the byproduct ratio is determined by 1 H NMR integration, while with L-AlMe 3 , a full condensation of Al-Me must be assumed in order to quantify the excess of SnMe4. A full description of the calculation procedure and the complete characterization data for all products are provided in the Supporting Information (Sections S2 and S3, respectively).