Five and Six-Coordinated Si-O Compounds

The best-known compound containing Si(VI) is the high-pressure silica polymorph stishovite, which has a chemical shift of 191.3 ppm (Stebbins and Kanzaki 1991). Other high-pressure silicate phases also known to contain Si( VI) are shown in Table 4.4, together with their Si chemical shifts. 

The group electronegativity approach (Janes and Oldfield 1985) also gives a reasonably good fit to the data (apart from that for Mg-Si perovskite), leading to the linear relationship for Si(VI) compounds 

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