Metal Complexes with Tetrapyrrole Ligands, LXV [1] . Generation and ESR Spectra of the Cation Radicals of Bis(octaethylporphyrinato)zirconium(IV) and Bis(chelate)(octaethylporphyrinato)zirconium(IV) Complexes

Electron spin resonance spectra of the cation radicals A + and B + generated from a zirconium(IV) monoporphyrin, bis(acetato)(octaethylporphyrinato)zirconium(IV), Zr(OEP)(OAc) 2 ( A ), and bis(octaethylporphyrinato)zirconium(IV), Zr(OEP) 2 ( B ), respectively, have been measured at 293 and 77 K. [Zr(OEP*)(OAc) 2 ]Br ( A + Br – ) has been prepared in situ by oxidation of A with bromine, [Zr(OEP √/2 ) 2 ]PF 6 ( B + PF 6 – ) by electrochemical oxidation of B . ESR parameters at 293 K are as follows: A + Br – : g = 2.0025, Δ H pp = 0.57 mT; B + PF 6 – : g = 2.0024, Δ H pp = 0.39 mT. The ratio of the line widths Δ H pp ( A + ) and Δ H pp( B + ) of the ESR signals of A + and B + is 1.46 at room temperature, i. e. very close to the value of √2 expected for a defect electron completely delocalized between the two porphyrin π electron systems in [Zr(OEP */2 ) 2 ] + . The ESR signal of A + Br – persists on cooling to 77 K excluding any kind of π‐π dimer formation. Treatment of (octaethylporphyrinato)bis(2,4‐pentanedionato)zirconium(IV), Zr(OEP)(acac) 2 , with bromine yields bis(3‐bromo‐2,4‐pentanedionato)(octaethylporphyrinato)zirconium(IV), Zr(OEP)(Bracac) 2 .