Ab initio RHF and density functional B3LYP and B3PW91 study of (NPF2)n; n=2,3,4 and (NPX2)3; X = H, Cl, Br cyclic phosphazenes

Molecular structure and bonding, thermochemical stability, and vibrational and NMR spectra of (NPF2)(n); n = 2,3,4 and (NPX2)(3); X = H, Cl, Br cyclic phosphazenes have been studied employing quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods using 6-31G, 6-31G* and 6-31 + G* basis sets. This study showed that these compounds have planar structure and, except for (NPH2)3, all are thermodynamically stable in the gas phase. Fluorophosphazenes (NPF2)(n) are found to be more stable than other phosphazenes. Furthermore, the identical values obtained for all P-N bond lengths in (NPX2)(3), with X = H, F, Cl and Br, phosphazenes suggests that the pi-bond system of the ring in this series of compounds has aromatic character. This is approved by high values of cross electron density between indirectly bonded atoms of the ring obtained in a population analysis carried out on these systems. (C) 2003 Elsevier B.V. All rights reserved.