Silyl radical crystal structure

Crystal structure analysis of 43 revealed that the radical is perfectly trigonal planar, implying the sp -hybridization of the central Si atom and, hence, the localization of the unpaired electron on its 3pz-orbital. The remarkable planarity of the radical 43 was explained by the great steric bulk of the voluminous t-Bu2MeSi groups, which prefered to move away from each other as far as possible to avoid the steric repulsion between them. On the contrary, the significant electron donation of the positive silyl substituents... 

The crystal structures of two isolable silyl radicals have recently been reported. The bulky substituted (t-Bu2MeSi)3Si radical was isolated as air-sensitive yellow needles [13], whereas the conjugated and bulky substituted cyclotetrasi-lenyl radical 15 was obtained as red purple crystals [51]. 

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