Using the estimated fractional abundances of the conformers (Table -2) and the calculated chemical shifts (Table -3), Boltzmann-averaged chemical shifts for compounds 12, 14, 18 and 22 were calculated (Figure , Table ). Due to the relatively low Gibbs energy differences for the extended conformers of 12 and 22 in the solvent phase compared to the most stable hypercoordinate conformer, the corresponding calculated Sn NMR chemical shifts are more approximate; higher energy non-hypercoordinate conformers would also need to be considered in the average. The Boltzmann averaged 119 Sn NMR chemical shifts for the gas phase geometries agree well with the experimental values, falling essentially on the linear correlation (Figure ). The values for the compounds calculated with the chloroform solvent model are significantly lower. On this basis, the PBE0-GD3BJ gas phase model appears to more accurately predict the conformer geometries/relative energies than the solution phase PCM: the condensed phase calculations seemingly overestimate the extent of hypercoordination and systematically underestimate the Sn-O distances. This points to a potential weakness in the "structural benchmarking" approach that has not been previously identified. The PBE0-GD3BJ method was originally selected on the basis of giving the best structural predictions for Sn hypercoordinate compounds in comparison with solid-state X-ray crystallographic structures. This approach may inadvertently factor in the effects of a condensed phase on relatively compressible interactions, such as the Sn-O hypercoordination, such that if the gas-phase calculation approximates it, a solution-phase calculation with the same functional will overestimate the strength and underestimate the distance. This suggests that alternative approach(s) are required for accurately modelling hypercoordinate interactions in solution. The tosyl-containing polystannane 24, as previously described, was prepared via a transition metal-catalyzed dehydrocoupling of 20 in a foil-wrapped Schlenk flask under a N2 atmosphere (Scheme 3). These precautions are to (i) avoid the possibility of light degrading the monomer, (ii) suppress homolytic cleavage of the resulting polystannanes and (iii) prevent the formation of stannoxanes from nucleophilic attack by moisture, respectively. Polymer 24 was purified by precipitation of a THF solution (3 mL) containing crude 24 into an excess of hexanes (100 mL) and thereafter recovered as an orange-coloured solid. GPC analysis in THF revealed a molecular weight (Mw) of 17 kDa and a Ð of 1.26. The tosylated polymer 24 was also characterized by both 1 H and 119 Sn NMR (C6D6) spectroscopy and was in agreement with the reported literature values. A similar dehydrocoupling reaction of 22 was successfully carried out to yield polymer 25 which was recovered as a yellow coloured powder in moderate yields (64 %). A molecular weight determination of 25 after purification proved difficult as the polymer was almost completely insoluble in THF, the solvent required for analysis. Attempts to redissolve purified 25 in the original reaction solvent also proved futile, and all analyses were thus carried with crude 25 due to the apparent highly crystalline nature of the resulting polymer. NMR ( 119 Sn) analysis of the crude polystannane 25 prior to purification reveal evidence of partial hypercoordination with two nearly equally intense resonances at δ = -193 and -238 ppm (Figure ), similar to what was observed for the phenyl propyl hydroxyl stannane polystannane, 27 (Figure ). After a single purification, the polymer is notably less soluble and displays only a single 119 Sn resonance at -237.9 ppm (Figure ), suggesting that the polymer likely migrates to a fully "closed" form. DSC analysis of homopolymer 25 reveals reversible semi-crystalline/highly crystalline character with Tm = 127 °C, and Tg = 91 °C (Figure ), similar to that for 27 (Tm = 110 °C, and Tg = 49 °C) as previously reported. The PXRD diffractogram of 25 (Figure ) shows five distinct signals. Two of the signals are intense and sharp in nature with 2θ values of 14.30° and 17.15°, while the remaining three signals are broad and less intense (2θ values of 6.35°, 18.93° and 25.90°). These values fall within the same range as other recently reported unsymmetrical polystannanes. The sharp signals in the PXRD diffractogram, in conjunction with the presence of a Tm in the DSC thermogram confirm that 25 is semi-to highly-crystalline in nature. Attempts to prepare the thioacetyl homopolymer 26 from 23 under similar protocols were unsuccessful owing largely to the extreme sensitivity of the polymer to light, which changed from a light yellow to a darker insoluble brown solid after a minimal exposure to light. Further explorations of this material were therefore abandoned.