DFT STUDY OF MOLECULAR STRUCTURE OF 5,10,15,20-TETRAKIS(4’-HALOGENOPHENYL)PORPHYRINS AND THEIR ISOMERS

Abstract

Conformational manifold of 5,10,15,20-tetrakis(4¢-halogenophenyl)porphyrins (p-4C6H4X-H2P; X=F, Br) was studied by DFT calculations (functional B3LYP). The conformers are different by positions of -4C6H4X groups relative to the macrocyclic core. Relative energies of the conformers of 4C6H4F-H2P were calculated with use of different basis sets in order to find the optimal ratio «quality/ computational cost». According to the results of the calculations, conformers of C2V symmetry are the most energetically favorable. However, relative energies of other conformers are quite low, therefore they should be taken into account at the treatment of the gas-phase electron diffraction (GED) experimental data. The sensitivity of the GED method to structural changes induced by different relative positions of halogenophenyl substituents was examined. Model radial distribution curves f(r) for conformers of p-4C6H4X-H2P, as well as meta- and ortho- isomers (m-4C6H4X-H2P and o-4C6H4X-H2P) were compared. The results of the model studies demonstrate that the bond distances can be reliably determined from experimental data, while the refinement of the positions of halogenophenyl substituents relative to the macrocyclic core is at the limit of the possibilities of the GED method. Meta- and ortho- isomers of 4C6H4X-H2P can be distinguished based on the experimental data, especially in the case of bromine-substituted phenyl groups.