Analysis of UV and vibrational spectra (FT-IR and FT-Raman) of hexachlorocyclotriphosphazene based on normal coordinate analysis, MP2 and DFT calculations

The Raman (1400–100 cm−1) and infrared (4000–400 cm−1) of solid hexachlorocyclotriphosphazene, P3N3Cl6 (HCCTP) were recorded. The conformational energies were calculated using MP2 and DFT (B3LYP and B3PW91) methods utilizing a variety of basis sets up to 6-311+G(d). On the basis of D3h symmetry, the simulated vibrational spectra of P3N3Cl6 from MP2 and DFT methods were in excellent agreement with those obtained experimentally. Additionally, Frontier Molecular Orbitals and electronic transitions were predicted using steady state and time dependent DFT(B3LYP)/PCM calculations respectively, each employing the 6-311+G(d,p) optimized structural parameters. The predicted wavelengths were in excellent agreement with experimental values when CH2Cl2 was used as solvent. The 14N and 31P chemical shifts were predicted with B3LYP/6-311+G(2d,p) calculations using the GIAO technique with solvent effect modeled using the PCM method. The computed structural parameters of the planar P3N3Cl6 (D3h) agree well with experimental values from both X-ray and electron diffraction data with slight distortions observed due to lattice defects in the solid phase. The experimental/computational results favor a slightly distorted D3h symmetry for the title compound in the gas and solid phases and in solution (τPNPN and τNPNP ranged from 0.018° to 0.90°). Aided by normal coordinate analysis, and the simulated vibrational spectra utilizing MP2, B3LYP and B3PW91 methods at 6-31G(d) basis set, revised and complete vibrational assignments for all fundamentals are provided herein.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► We carried out MP2, B3PW91 and B3LYP geometry and frequency calculations for hexachlorocyclotriphosphazene, P3N3Cl6. ► Experimental vibrational data are consistent with simulated spectra using MP2, B3PW91 and B3LYP methods at 6-31G(d). ► 15N and 31P chemical shifts are predicted with good agreement with available experimental values. ► Electronic transitions, HOMO and LUMO MOs were calculated using TD-DFT/PCM employing B3LYP/6-311+G(d,p) SPs. ► Computational and experimental results favor a slightly distorted D3h symmetry of P3N3Cl6 in all phases.