Difluorenylsilane derivatives, a class of compounds exhibiting strong intra- and intermolecular CH⋯π interactions. Crystal and molecular structures of bis(9-methylfluoren-9-yl)dimethylsilane and (9-methylfluoren-9-yl)(fluoren-9-yl) dimethylsilane

The crystal and molecular structures of substituted difluorenyl-(dimethyl)silanes Me2Si(CR′R2)(CR″R2) (R′=H, R″=Me 1 and R′=R″=Me 2, CR2=fluorenyl) have been determined by X-ray diffraction and compared with the conformations available in the gas phase. 1 and 2 crystallize in the P2(1)/m and P2(1)/c space groups with the cell parameters: a=7.191 Å, b=17.658 Å, c=8.982 Å, α=γ=90°, β=101.880° (1) and a=13.132 Å, b=7.463 Å, c=24.438 Å, α=γ=90°, β=99.73° (2), respectively. Both compounds as well as the unsubstituted parent silane Me2Si(CHR2)2 (3) exhibit extensive intramolecular and intermolecular CH⋯π interactions leading to supramolecular associations. Gas phase conformations predicted on the basis of AM1 semiempirical molecular orbital calculations support the existence of these intramolecular interactions and correlate well with the temperature dependent proton NMR spectra.