The silicon atom is pentacoordinate in cations of salts like 1, which can be prepared, for instance, in a redox reaction of the corresponding silane (with I2, X = I) or transformation with electrophiles like PhCoCl (X = Cl) or Ph3C+BF (X= BF4). These compounds were completely characterized; conductivity titrations confirm that they are ionic.
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Chuit et al. (1993) studied this question.
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