Interactions in crystals. 139. Biphenylene ring expansion by a (H3C)(2)Si link from silicone grease as proven by the crystal structures of [(sodium(+)[2.2.1]cryptand)(9,9-dimethylsilafluorene(center dot-))] as well as [sodium(+)(triglyme)2(biphenylene(center dot-))] and by total-reflection X-ray fluroescence spectrometry (TXRF)

Sodium metal mirror reduction of biphenylene in aprotic THF solution, conta ining [2.2.1]cryptand yields as a structurally characterized product the 9, 9-dimethylsilafluorene radical anion salt containing a (H3C)(2)Si expanded cyclobutadiene ring. In addition, the Si content cart be detected by total reflection X-ray (TXRF) analysis. When the use of any silicon grease was av oided for all glass fittings, the solvent-separated biphenylene radical ani on contact pair crystallized from an aprotic diglyme solution.