Of a variety of the organosilicon compounds, silole (silole = silacyclopentadiene) derivatives have attracted much attention in material science owing to their various applications to conductors, OLEDs (organic light-emitting diodes) and nonlinear optics. 1 By introducing various functional groups at the 2 and 5 positions, siloles have been shown to have unique electronic properties and novel molecular structures. Based on previous reports, a series of siloles with the same functional group at

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... he 2 and 5 positions were prepared readily by a Pdmediated one-step reaction via intramolecular reductive cyclization when employing bis(alkyl or arylethynyl)silanes. 2 Although the crystal structures and optical properties of 2,5disubstituted siloles, containing the same group at the 2 and 5 positions, have been well described in the past several years, the number of analyzed structures of silole with different groups at those positions, such as 2-alkyl-5-arylsilole, 2-halo-5-alky(or aryl)silole and 2-alky(or aryl)-5H-silole etc., still remains limited. In our ongoing development of silole derivatives, 3 we found that mono-substituted siloles at the 2 or 5 position were formed as major components, depending on reaction conditions. Herein, we describe the structure of mono-substituted silole, 2biphenyl-2-yl-1,1,3,4-tetraphenyl-1H-silole (Fig. 1) , based on an X-ray crystal analysis. 2-Biphenyl-2-yl-1,1,3,4-tetraphenyl-1H-silole was prepared by a slight modification of the synthetic methodology reported by Tamao's group. 2 Pale-yellow crystals suitable for X-ray crystallography were grown by slow evaporation from dichloromethane/hexane at room temperature. The crystal and experimental data are depicted in Table 1 . The structure was solved by a direct method. The bond length of C2-C18 is 1.498(6)Å, which is slightly longer than those of other 2,5diarylsiloles, such as 1,1-dimethyl-2,5-bis(p-nitrophenyl)-3,4diphenylsilole (1.475(2)Å), 1,1-dimethyl-2,5-bis(p-x81 ANALYTICAL SCIENCES 2004, VOL. 20 X-ray Structure Analysis Online Crystals of silole (silole = silacyclopentadiene) analogue, 2-biphenyl-2-yl-1,1,3,4-tetraphenyl-1H-silole, were grown from a dichloromethane/hexane solution and the crystal structure was determined. The crystal belongs to the monoclinic system with space group of P21/c. There is an intramolecular π-π interaction in an asymmetric unit, and the shortest distance between one of the phenyl rings in the biphenyl and the phenyl ring at the 3-position of silole is about 3.643 Å. This silole can be used as a potential building block for generating linear polymers containing the silole moiety owing to the labile nature of the proton attached at the 2-position.