Silicon hypervalent properties

Si NMR spectroscopy in solution and, increasingly, in the solid state has become an indispensable tool in the multi-faceted silicon chemistry. The Si NMR parameters are ideally suited to complement direct structural information from X-ray crystallography. Moreover they are extremely valuable in the investigation of dynamic properties both intermolecular and intramolecular. This includes the attractive chemistry of hypervalent silicon as well as the fascinating playground of low-coordinated silicon compounds. The excellent performance of modern NMR spectrometers has overcome most problems associated with the determination of Si NMR parameters. The trend towards a multinuclear approach in NMR spectroscopy is certainly fortified by the availability of Si NMR parameters. 

The first model of the bonding in silatranes invoked an sp d hybridization of the silicon atom . HowevCT, this theoretical scheme was of very limited anal3dical value for understanding the silatrane properties. Moreover, many experimental and quantum chemical data ruled out the valence role of d orbitals in molecules of main group elements . In 1977 the Musher model of hypervalency was modified with reference to the Group 14 elements and used for a quahtative analysis of the structural trends in silatranes . 

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