Hexasilaprismanes structure

Figure 7 shows the ORTEP drawing of the hexasilaprismane 1237. Its structural parameters are listed in Table 4. The crystal has a two-fold axis of symmetry. The skeleton has a slightly distorted prismane structure with two triangular units [Si-Si = 2.374-2.387 A (av. 2.380 A) and ZSi-Si-Si = 59.8-60.3° (av. 60.0°)] and three... 

NMR spectroscopy is a powerful tool for structural analysis. The chemical shifts of polyhedral silicons range from —22 to 39 ppm. The 29Si chemical shifts of tetrasilatetrahedrane ll32, hexasilaprismane 1237 and octasilacubanes (163, 18a44b, 18b45, 2046 and 2247) are listed in Table 10. 

Because H-Si-SiHs is nearly isoenergetic with H2Si = SiH2, it is not obvious which structure would be favored for hexasilabenzene, SieHe. Whereas proponents of aromaticity may take heart from the theoretical calculations that show the hexasilabenzene structure to be 34 kcal/mol more stable than the tris(silylene) form, they will be reminded of how little aromaticity has to do with the magic of six tt electrons by the revelation that the hexasilaprismane is calculated to be 14 kcal/mol more stable yet. 

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