Chemical Bonding in Phosphonitrilic Systems-Comparison of the Electronic Structures of (F Sub 2 PN) sub 3 , (F Sub 2 PN) sub 4 , and OP(F sub 2 )NP(F sub 2 )NPF sub 3.

摘要

The electronic structure of phosphonitrilic systems contain both pi ' (in-plane) and pi (out-of-plane) bonding systems. Earlier work in this laboratory has indicated that the d-orbital involvement in these systems affects primarily the electronic structure, and is modulated by ligand electronegativity. Ab initio molecular orbital calculations were performed on a series of small phosphazene molecules ((F2 PN)3, (F2 PN)4 and OP(F2)NP(F2)NPF3) to elucidate the electronic and molecular structure of these small molecules as models for polymeric systems. The chemical bonding and charge distribution in the phosphonitrilic trimers, tetramers and these small fragments is highly polarized, primarily through the pi and pi ' bonding networks. Our results indicate that while the majority of the electronic aspects of OP(F2)NP(F2)NPF3 can be described by analogies to (F2PN)3 and (F2PN)4, major geometric differences such as bond alternation are evident. The opening of the P-N-P bond angles in the linear fragment results in reduced overlap over multiple centers, promoting ''islands of delocalization'' first proposed by Dewar et al. 18 refs., 3 figs., 3 tabs.