Isomerism in dihalogenometal porphyrins and phthalocyanines: a theoretical study of dihalogenotitanium complexes

Abstract

Trans- and cis-isomers of dihalogenotitanium porphyrins and phthalocyanines, TiX₂P and TiX₂Pc (X = F, Cl, Br, I; P = porphyrin, Pc = phthalocyanine), which provide a good example of isomerism in dihalogenometal porphyrin and phthalocyanine complexes, have been studied by density functional theory calculations using the B3LYP hybrid method and triple-ζ valence basis sets. All eight complexes have two isomers, trans-isomer of D _4h symmetry and cis-isomer of C _2v symmetry with halogen atoms located in the same plane with two meso-atoms. In the case of difluorotitanium phthalocyanine the cis-isomer is preferable in the gas phase, while in all porphyrin complexes and remaining three phthalocyanine complexes the trans-isomers have lower energies than cis-isomers. Electrostatic repulsion between the halogen atoms and central nitrogen atoms of the macroheterocycle seems to play the major role in determining the preference of the trans- or cis-isomer.

Keywords:

• porphyrin
• phthalocyanine
• titanium
• isomerism
• density functional calculations

Acknowledgements

The author is grateful to Professor Mikhail K. Islyaikin (Department of Fine Organic Synthesis, Ivanovo State University of Chemistry and Technology) for valuable suggestions and discussion.