The influence of hydrogen bond on the structure and IR spectrum of triphenyl phosphite

Background and Objectives: The IR spectra of triphenyl phosphite (TPP) have been measured at temperatures of 12 and 320 K in five phase states: crystalline (monoclinic and hexagonal phases), “glacial”, amorphous and liquid. It is necessary to clarify the effect of hydrogen bonding on the structure and IR spectrum of TPP. Materials and Methods: The IR spectra were measured on the IFS-88 spectrophotometer using the OPUS software. The spectral resolution was 2 cm$^{-1}$. The energies, geometrical structures, mechanical and electro-optical parameters of the TPP H-complex represented by dimer were calculated using the density functional theory method B3LYP/6-31G(d) implemented in the Gaussian 03 program package. Results: The studies indicate the presence of the weak H-bonding С$_{12}$-Н$_{15}\cdots$О$_{41}$ between the PO$_3$ group and benzene ring. The energy of the Н-bond is 1.3 kcal/mol. The length of the hydrogen bridge is 2.963 Å. The dipole moment is 4.5 D. The H-bond only affects the vicinity of the hydrogen bridge. Influence of the H-bond is not significant for the frequencies, but the intensities change more significantly. The presence of the H-bond is confirmed by the changes at 715-740, 850-890, 1180-1220, 3020-3080 cm$^{-1}$ regions. Conclusions: Investigations of the measured IR spectra and the results of computer simulation confirmed the presence of weak H-bond in the TPP samples. With its help, conformers are combined into dimers and trimers. The H-bond affects the structure of the conformer fragment $P(OС)_3$ and its spectral characteristics (bands at 715-740, 850-890, 1180-1220 cm$^{-1}$ regions changes) and changes the shape of the band in the region of stretching vibrations of C-H bonds (3020-3080 cm$^{-1}$) bringing it closer to the experimental ones. The TPP samples at liquid, amorphic, “glassial” states and crystal modifications are a mixture of different conformers and H-complexes with weak H-bond (dimers and trimers). The conformers and H-complexes determine the shape of IR spectra in different phase states.