CRYSTAL-STRUCTURE AND MOLECULAR MECHANICS, DYNAMICS AND QUANTUM-MECHANICAL AB-INITIO STUDIES OF 2,2,4,4,6,6-HEXAKIS(P-PHENOXYPHENOXY)-2-LAMBDA(5),4-LAMBDA(5),6-LAMBDA(5)-CYCLOTRIPHOSPHAZA-1,3,5-TRIENE

Molecular mechanics modelling and molecular dynamic (MD) simulations have been carried out for [NP(OC(6)H(4)OPh-p)(2)](3). Force-field parameters developed for cyclotriphosphazenes gave calculated bond lengths and angles in agreement with the values determined by X-ray diffraction analysis of the crystal. Calculated and X-ray diffraction data for the torsional angles were in poor agreement due to crystal-packing forces determining the conformation in the solid. The MD simulation gave a nearly symmetric equilibrium conformation and showed that the fluxional mobility of the phenoxy groups increases on going from the P-O bonds of the phosphazene core to the external fragments of the molecule. The crystals were triclinic, space group P ($) over bar 1, with a = 15.345(2), b = 15.440(3), c = 15.999(3) Angstrom, alpha = 80.43(1), beta = 66.67(1), gamma = 60.62(1)degrees and Z = 2, and the structure was refined to R = 0.057 and R' = 0.066. The force-field parameter set for MD well reproduces the energy difference between the solid and gas-phase conformations calculated by the ab-initio (STO-3G*) method. The calculated small energy differences between the molecular orbitals indicate a possible quasi-band structure for the bonding electrons. A perturbation of the electronic system localized on the atoms of the external phenyl groups can therefore propagate towards the P and N atoms of the cyclophosphazene ring.