Журнал "Макрогетероциклы"

^aIvanovo State University of Chemistry and Technology, 153000 Ivanovo, Russia.

^bA.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Science, 119334 Moscow, Russia.

^cIvanovo State University, 153025 Ivanovo, Russia

^@Corresponding author E-mail: girichev@isuct.ru

 

DOI: 10.6060/mhc224109g
Macroheterocycles 2021 14(4) 334-341

 

Synthesis of two platinum complexes, 5,10,15,20-tetraphenylporphyrin (PtTPP) and 5,10,15,20-perfluorotetraphenyl-
porphyrin (PtTF₅PP), is described. IR spectra of the complexes and metal-free 5,10,15,20-tetraphenylporphyrin (H₂TPP) were obtained in KBr tablets. Structural parameters of conformers were optimized using DFT/B3LYP/cc-pVTZ (C,N,H,F), aug-cc-pVTZ-PP, ECP (Pt), and their vibration frequencies were calculated. Conformers differ mainly in angles of rotation of substituents at meso-position relative to macroheterocyclic backbone. For H₂TPP, the most stable conformer possesses C_2v symmetry, for PtTPP – D_2d , and for PtTF₅PP – D_4h . Energy difference between conformers of each molecule does not exceed 1.1 kJ/mol.

Experimental and theoretical IR spectra are presented, their comparison determines the scaling factor (0.977) for theoretical vibration frequencies of all three molecules in the range of 500–1700 cm^–1. Interpretation of experimental IR spectra has been performed. For all frequencies of normal vibrations, the potential energy distribution along the internal vibrational coordinates is analyzed. The spectra of the three compounds in the range of 2800–3400 cm^–1 differ from each other. The IR spectrum of the H₂TPP compound contains a band at 3370 cm^–1, which belongs to the stretching vibration ν(N-H), while the IRS of the PtTF₅PP compound lacks a band at 2925 cm^–1 belonging to the ν(С_Ph-H) vibrations of phenyl fragments. The frequencies ν(N-H), ν(С_b-H) and ν(С_Ph-H) correlate with the values of corresponding internuclear distances. The shorter the bond length, the higher the force constant of stretching of this bond and the higher the frequency of the stretching vibration. Introduction of platinum atom into coordination cavity changes the relative intensity of bands in region of 500–1700 cm^–1 and decreases their number, which is associated with an increase in the symmetry of PtTPP and PtTF₅PP molecules as compared to H₂TPP. Most of vibrational modes in the region of 500–800 cm^–1 are mixed and represent a linear combination of several internal coordinates. They refer to nonplanar out-of-plane vibrations of macroheterocyclic backbone, as well as to nonplanar deformations of carbon skeleton in the –C₆H₅ and –C₆F₅ substituents. Frequencies in the range 900–1600 cm^–1 mainly refer to stretching vibrations of C_a-C_b, C_Ph-C_Ph, C_a-C_m, C_a-N, C-F bonds, as well as to plane and non-planar vibrations associated with a change in bond angles of C_a-C_b-H in the backbone and C_Ph-C_Ph-H angles in the –C₆H₅ substituents. The calculated IR spectra in the low-frequency region up to 500 cm^–1 reflect the structural nonrigidity of molecules and correspond to vibrations at which the macrocyclic backbone of the dome, raffling, and wave type is distorted, as well as distortions occurring in plane of the backbone. The same region contains the frequencies of torsional vibrations of –C₆H₅ and –C₆F₅ substituents. Difference in the IR spectra is considered and the characteristic frequencies of three compounds are determined. A distinctive feature of IR spectrum of PtTF₅PP is the presence of intense absorptions, which belong to C-F stretching vibrations of different symmetry, and which are absent in IR spectra of H₂TPP and PtTPP. H₂TPP spectrum contains a band at 883 cm^–1, which is associated with a combination of vibrational coordinates r(C_a1-C_b1) and r(C_a2-C_b2) in two nonequivalent fragments. This band is absent in the IR spectrum of platinum complexes.

The relationship between the geometric parameters and frequencies of stretching vibrations of H₂TPP, PtTPP, and PtTF₅PP molecules is shown.