X-ray powder diffraction characterization of the elusive tetraphosphine Si(CH2PPh2)4 silane

X-ray powder diffraction data for the tetraphosphinic Si(CH2PPh2)4 silane are reported. Its crystal and molecular structures were determined by simulated annealing and full-profile Rietveld refinement methods. Si(CH2PPh2)(4) was found to have tetragonal symmetry with P-42(1)c space group. The lattice parameters were determined to be a = 17.211(2) angstrom, c = 7.553(1) angstrom, V = 2237.5(5) angstrom^3. The crystal structure was found to contain isolated Si(CH2PPh2)(4) molecules. In each Si(CH2PPh2)(4) molecule, the central Si atom was fixed at the -4 symmetric position bearing four CH2PPh2 branches. This environment was confirmed by P-31 CP/MAS NMR measurements. Thermo-diffractometric measurements in the 20-120 degrees C range were also used to estimate the linear and volumetric thermal expansion coefficients (d ln V/ dT=1.8 x 10^-4 K^-1, typical for very "soft" materials.