METAL COMPLEXES WITH TETRAPYRROLE LIGANDS .65. 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+ gen erated from a zirconium(IV) monoporphyrin, bis(acetato)(octaethylporph yrinato)zirconium(IV), Zr(OEP)(OAc)(2) (A), and bis(octaethylporphyrin ato)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)]PF6 (B+PF6-) by electrochemical oxidation of B. ESR parameters at 293 K are as follow s: A(+)Br(-): g = 2.0025, Delta H-pp = 0.57 mT; B+ PF6-:g =2.0024, Del ta H-pp, = 0.39 mT. The ratio of the line widths Delta H-pp(A(+)) and Delta Hpp(B+) of the ESR signals of A(+) and B+ is 1.46 at room temper ature, i.e. very close to the value of root 2 expected for a defect el ectron completely delocalized between the two porphyrin phyrin pi elec tron systems in [Zr(OEP(./2))(2)](+). The ESR signal of A(+)Br(-) pers ists on cooling to 77 K excluding any kind of pi-pi dimer formation. T reatment of porphyrinato)bis(2,4-pentanedionato)zirconium(IV), Zr(OEP) (acac)(2), with bromine yields tanedionato)(octaethylporophyrinato)zir conium(IV), Zr(OEP)(Bracac)(2).