Redox-Driven Symmetry Change for Terbium(III) Bis(porphyrinato) Double-Decker Complexes by the Azimuthal Rotation of the Porphyrin Macrocycles

Ken-Ichi Yamashita; Takayo Yamanaka; Naoya Sakata; Takuji Ogawa

doi:10.1002/asia.201800324

Redox-Driven Symmetry Change for Terbium(III) Bis(porphyrinato) Double-Decker Complexes by the Azimuthal Rotation of the Porphyrin Macrocycles

Chem Asian J. 2018 Jul 4;13(13):1692-1698. doi: 10.1002/asia.201800324. Epub 2018 May 9.

Authors

Ken-Ichi Yamashita¹, Takayo Yamanaka¹, Naoya Sakata¹, Takuji Ogawa¹

Affiliation

¹ Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka, 560-0043, Japan.

PMID: 29575725
DOI: 10.1002/asia.201800324

Abstract

Molecular structures for three oxidation forms (anion, radical, and cation) of terbium(III) bis(porphyrinato) double-decker complexes have been systematically studied. We found that the redox state controls the azimuthal rotation angle (φ) between the two porphyrin macrocycles. For [Tb^III (tpp)₂ ]ⁿ (tpp: tetraphenylporphyrinato, n=-1, 0, and +1), φ decreases at each stage of the oxidation process. The decrease in φ is due to the higher steric repulsion between the phenyl rings on the porphyrin macrocycle and the β hydrogen atoms on the other porphyrin macrocycle, which results from the shorter interfacial distance between the two porphyrin macrocycles. Conversely, φ=45° for both [Tb^III (oep)₂ ]^-1 and [Tb^III (oep)₂ ]⁰ (oep: octaethylporphyrinato), but φ=36° for [Tb^III (oep)₂ ]⁺¹ . Theoretical calculations suggest that the smaller azimuthal rotation angle of the cation form is due to the electronic interaction in the doubly oxidized ligand system.

Keywords: lanthanides; porphyrinoids; redox chemistry; sandwich complexes; structure elucidation.