Hexasilaprismane, calculations

The static solid-state NMR can produce a broad pattern to give the three principal values of the shielding tensors for polyhedral silicons. Figures 15 and 16 show the static powder spectra of octasilacubane 22 and of the hexasilaprismane 12, respectively56. The values of the an, 022 and <733 tensors are given in Table 11 together with the calculated values for the methyl substituted compounds57. 

TABLE 11. Experimental and calculated principal values of shielding tensors for hexasilaprismane and octasilacubane... 

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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