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

Abstract

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-421c space group. The lattice parameters were determined to be a=17.211(2) Å, c=7.553(1) Å, V=2237.5(5) Å3. 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 31P CP/MAS NMR measurements. Thermo-diffractometric measurements in the 20–120 °C range were also used to estimate the linear and volumetric thermal expansion coefficients (∂ ln V/∂T=1.8×10−4 K−1), typical for very “soft” materials.