title: The origin of endocyclic bond length variations in disubstituted cyclotriphosphazenes.
abstract: Intraannular ring alternation in heterogeneously substituted cyclotriphosphazenes is investigated using both ab initio and density functional methods. Comparisons of the calculated geometries for N3P3X6 (X = H, F, Cl, Me, Ph) and N3P3X4Y2 (X = F, Cl; Y = Me, Ph, X, Cl) with experimental X-ray data establish the utility of the 6-31G* basis for use with both Hartree-Fock and the B3LYP and B3PW91 functionals. Analysis of orbitals and charges shows that the bonding is best described using a polarized bond model rather than the previous explanation of asymmetric nitrogen-lone-pair donation into the phosphorus-nitrogen bond.
authors.affiliation: Department of Chemistry, University of Vermont, Burlington, Vermont 05405-0125, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Calichman
authors.forename: Agnes
authors.initials: A
authors.lastname: Derecskei-Kovacs
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Allen