DFT study of the structure and IR spectra of Gc1 model compound built from cyclotriphosphazene core

The infrared (400-4000 cm−1) spectra have been recorded in the crystalline state and in the melt for hexakis(4-N′-dichloro(thio)phosphonyl)-N′-methyl-diazobenzene)cyclotriphosphazene (Gc1) which models the structure of dendrimer built from cyclotriphosphazene core. An X-ray diffraction study of Gc1 was undertaken for the first time in order to understand why it is possible to obtain phosphorus dendrimers of high generations starting from cyclotriphosphazene core. Besides triphosphazene cycle constituting the core, Gc1 possess also six C6H4CHNN(CH3)P arms and terminal PCl groups. The structural optimization and normal mode analysis are performed for Gc1 molecule on the basis of the density functional theory (DFT). It is found that Gc1 built from cyclotriphozphazene core has a concave lens structure. The Gc1 molecules exist in a single stable conformation with planar OC6H4CHNN(CH3)P fragments and slightly non-planar cyclotriphosphazene core. All these observations suggest that terminal groups are readily available for further reactions. Relying on DFT calculations a complete vibrational assignment is proposed for different parts of the studied molecule.