PENTACOORDINATED MOLECULES .34. STRUCTURAL CHARACTERIZATION OF CHLOROSPIROPHOSPHORANES EXISTING AS NEARLY PERFECT RECTANGULAR PYRAMIDS

Single-crystal x-ray analysis of 2,3-benzo-7,8-tetrachlorobenzo-l,4,6,9-tetraoxa-5-phenyl-5λ5-phosphaspiro[4.4]nona-2,7-diene, (C6Cl4O2)(C6H4O2)P(C6H5), VI, and 2,3,7,8-bis(tetrachlorobenzo)-5-phenyl-l,4,6,9-tetraoxa-5λ5-phosphaspiro[4.4]-nona-2,7-diene, (C6Cl4O2)2P(C6H5), VII, showed that they possessed nearly perfect rectangular-pyramidal geometries. The distortion amounts to only 6% for each as measured by the sum of dihedral angles, and the direction of structural displacement is on a coordinate leading to a connecting trigonal-bipyramidal isomer. Data for both compounds were collected on an Enraf-Nonius CAD4 automated diffractometer, by using Mo K radiation, out to a maximum 2λMoKa of 55°. VI crystallizes in the triclinic space group PĪ, with a = 8.495 (1) Å, b = 9.866 (1) Å,c= 12.053 (2) Å, α = 76.22 (1)°, β = 71.38 (1)°, γ = 88.95 (1)°, and Z = 2. Full-matrix least-squares refinement gave R = 0.029 and Rw = 0.039 for the 2980 reflections having I ≤ 3σI, VII crystallizes in the triclinic space group PI, with two phosphorane molecules and one chlorobenzene molecule, which is disordered about an inversion center, per unit cell. The lattice constants are a = 8.242 (4) Å, b = 12.806 (2) Å, c = 12.821 (3) Å, α = 72.76 (2)°, β = 76.78 (3)°, and γ = 75.58 (3)°. Full-matrix least-squares refinement gave R = 0.048 and RW = 0.067 for the 3331 reflections having I ≥ 3σI. The close approach to an ideal rectangular bipyramid for each of these spirocyclics is aided by the electron-withdrawing effect of the chlorine ring substituents and their symmetrical placement. © 1979, American Chemical Society. All rights reserved.