PENTACOORDINATED MOLECULES .34. STRUCTURAL CHARACTERIZATION OF CHLOROSPIROPHOSPHORANES EXISTING AS NEARLY PERFECT RECTANGULAR PYRAMIDS (REPRINTED FROM INORG CHEM, VOL 18, PG 1668, 1979)

Single-crystal X-ray analysis of zo-7,8-tetrachlorobenzo-1,4,6,9-tetra oxa-5-phenyl- 5 lambda(5)-phosphaspiro[4,4]nona-2,7-diene, (C6Cl4O2)(C 6H4O2)P(C6H5) VI, and -bis(tecrachlorobenzo)-5-phenyl-1,4,6,9-tetraoxa -5 lambda(5)-phosphaspiro[4,4]-nona-2,7-diene, (C6Cl4O2)(2)P(C6H5), VI I, showed that they possessed nearly perfect rectangular-pyramidal geo metries. 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 autom ated diffractometer, by using Mo K alpha radiation, out to a maximum 2 theta(MoK alpha) of 55 degrees. VI crystallizes in the triclinic spac e group <P(1)over bar>, with a = 8.495 (1) Angstrom, b = 9.866 (1) Ang strom, c = 12.053 (2) Angstrom, alpha = 76.22 (1)degrees, beta = 71.38 (1)degrees, gamma = 88.95 (1)degrees, and Z = 2. Full-matrix least-sq uares refinement gave R = 0.029 and R(w) = 0.039 for the 2980 reflecti ons having I greater than or equal to 3 sigma(I). VII crystallizes in the triclinic space group <P(1)over bar>, with two phosphorane molecul es and one chlorobenzene molecule, which is disordered about an invers ion center, per unit cell. The lattice constants are a = 8.242 (4) Ang strom, b = 12.806 (2) Angstrom, c = 12.821 (3) Angstrom, alpha = 72.76 (2)degrees, beta = 76.78 (3)degrees, and gamma = 75.58 (3)degrees. Fu ll-matrix least-squares refinement gave R = 0.048 and R(w) = 0.067 for the 3331 reflections having I greater than or equal to 3 sigma(I). Th e close approach to an ideal rectangular bipyramid for each of these s pirocyclics is aided by the electron-withdrawing effect of the chlorin e ring substituents and their symmetrical placement.