Abstract

The formation of cyclophospazenes containing several ligands or substituent groups gives rise to an attractive derivative set, for development of novel applications, with variable properties. Here, it is possible to unravel the role of different functional groups attached to the N3P3 backbone, to reach a better understanding of the bonding character in the cyclic [PN] skeleton. We employed the extended transition state-natural orbital for the chemical valence scheme to unravel the sigma and pi orbital kernels that are involved in the assembling of such structures, by varying the acceptor-donor characteristics of the CF3, NO2, COOH, CN, NH2, OH, and OCH3 groups, where NO2 behaves as a stronger electron-withdrawing substituent rather than CF3, COOH, and CN, denoting that the nature of the ligand-phosphazene interaction contributes to some degree to the bond strength of the cyclic [PN] backbone. Our results reveal that the electron-withdrawing NO2 group leads to higher sigma and pi [PN] orbital-energy contributions, which is reflected in a shortening of the [PN] distance, contrasting with the case of electron-donating groups such as NH2, OH, and OCH3 within the phosphazene set. These insights allow further variation and modulation of the bonding in the [PN] ring.