Solid-state structure and solution conformation of 2,2,4,4,6,6,-hexa-(p-chlorophenoxo)cyclotri-λ5-phosphazatriene. X-Ray and dipole moment studies

Abstract

The crystal and molecular structure of [NP(OC₆H₄Cl-p)₂]₃ was determined by X-ray analysis. The dipole moments of this compound and its unsubstituted analogue [NP(OC₆H₅)₂]₃ were measured in benzene at 25 °C and interpreted in terms of the conformation in solution. Crystals of [NP(OC₆H₄Cl-p)₂]₃ are monoclinic with unit-cell dimensions a= 17.804(6), b= 7.656(3), c= 27.951 (9)Å, and β= 91.68(7)°; space group P2₁/c. The structure was determined from 2 418 three-dimensional counter data and refined to R= 0.051. The phosphazene ring is almost planar (maximum deviation 0.06 Å), and the mean bond distances and angles are P–N 1.575(5), P–O 1.579(5), and O–C 1.393(8)Å, P–N–P 122.5(3) and N–P–N 117.4(3)°. The conformations of the phenoxo-groups at P(3) are different from those at atoms P (1) and P(2) at which these groups adopt the same conformation. The measured dipole moment data for both compounds are in agreement with a C₃ symmetry conformation in which at each local O–P–O plane one phenoxo-group is rotated by ca. 40–50° from the anti-coplanar arrangement relative to this plane. These data also indicated that the conformation about the P–O bonds found in the crystal is not retained in solution.