METAL-COMPLEXES WITH TETRAPYRROLE LIGANDS .58. ZIRCONIUM(IV) AND HAFNIUM(IV) BISPORPHYRINATE DOUBLE DECKERS - SYNTHESIS, SPECTRA, REDOX POTENTIALS, AND STRUCTURE

The synthesis of new zirconium and hafnium bisporphyrinate double deckers M(P)2 (M = Zr, Hf; P = OEP, TPP)2,3) is described. The complexes are characterized by UV/Vis/NIR and H-1-NMR spectroscopy and cyclic voltammetry. As compared with M = Ce, the redox potentials or the energies of the near-infrared absorption bands of the corresponding radical cations [M(P)2]+ are lower by almost-equal-to 0.2 V or higher by almost-equal-to 2000 cm-1, respectively. Hence, there is a stronger pi-pi interaction between the porphyrin ligands as compared with the cerium analogues due to the smaller ionic radii of Zr(IV) and Hf(IV). X-ray crystallography of Zr(TPP)2 confirms the sandwich-like structure of the compound and the close proximity of the porphyrin ligands.