Crystal structure of the solid solution of 1,1,1-tris(diphenylphosphinomethyl)propane and its phosphine oxide analogs

The crystal and molecular structure of the solid solution of 1,1,1-tris(diphenylphosphinomethyl)propane and its phosphine oxide analogs C₄₂H₄₁O_0.64P₃ (I) was determined by X-ray diffraction analysis; space group P1, a = 10.945(3), b = 11.277(2), c = 15.985(6) Å, α = 76.10(2), β = 72.03(2), γ = 71.71(2)°, Z = 2. Structure I was solved by direct methods and refined by the full-matrix least-squares procedure in an anisotropic approximation to R = 0.045 for all 5227 unique measured reflections (CAD-4 automatic diffractometer, λCuK_α). Low-occupied phosphoryl O sites are found near each of the three P atoms in structure I. The total occupancy of the three O sites is 0.64(1), from which it follows that the contents of the - CH₂PPh₂ and - CH₂P(O)Ph₂ fragments in I are 78.6 and 21.4%, respectively. In averaged (mixed) molecule I, all P=O bonds were obtained effectively shortened, and the average P-C bonds P-C(sp³) and P-C(ar) equal 1.846 and 1.834 Å, respectively.