The 13 C, Si, and 31 P MAS ssNMR spectra were acquired in 4 mm ZrO2 rotors on a Bruker Avance NEO 700 MHz spectrometer with a MASDVT700S4 BL4 N-P/H probehead at 298 K. C CP/TOSS (176.21 MHz) MAS NMR spectra were obtained with 5 kHz MAS frequency, 500 µs contact time, 4 s delays, and 1 H CW decoupling. All 13 C ssNMR chemical shifts were referenced externally to adamantane (δ = 38.5 ppm). Si (139.23 MHz) and 31 P (283.69 MHz) MAS NMR spectra were obtained using the standard 90°-pulse experiment, with 12 kHz MAS frequency, and 60 s and 4 s delays for Si and 31 P, respectively. The 29 Si and 31 P ssNMR chemical shifts were referenced externally to DSS (δ = 1.5 ppm) and NH 4 H 2 PO 4 (δ = 1.0 ppm), respectively. The 29 Si ssNMR spectra were deconvoluted in SpinWorks 4.2.5 using two peaks (Lorentzian-Gaussian linear combination) centered around -101 (narrow) and -107 (broad) ppm, corresponding to [SnOSi] and [AlOSi] moieties of unreacted and reacted corners of the CUBE, respectively. The ratio of the two peaks was then used to independently calculate the spectroscopic degree of condensation DC N of the tin groups DC N (SnMe 3 ) for the purpose of validation of the combined gravimetry/ 1 H NMR approach. The calculation procedure (Table ), peak fitting data (Table ), and the resulting DC values (Table ) are provided in the Supporting Information.