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

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 [TbIII (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 [TbIII (oep)2 ]-1 and [TbIII (oep)2 ]0 (oep: octaethylporphyrinato), but φ=36° for [TbIII (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.