Peroxo complexes magnetic moments

The /u-peroxo dimer intermediate, C, in the oxidation of four-coordinate Fe porphyrins to the PFe-O FeP /U.-OXO dimer via equations (23A-C) (cf. Scheme 2) of tetrakis(m-tolyl)porphrnatoiron(III), has been detected by NMR spectroscopy at low temperatures. The /r-peroxo complex has a larger isotropic shift (16 vs. 13 ppm for the ii-0x0 dimer at -50 °C) for the pyrrole-H at all temperatures, and has an antiferromagnetic coupling constant, —27, that is about 30% smaller than that for the /r-oxo dimer, E the magnetic moment decreases from 2.6/tb at —50°C to about 2.2/tb at —80°C, both consistent with weaker antiferromagnetic coupling in the /u-peroxo complex. ... 

A number of investigations of the magnetic susceptibility of the peroxo compounds have been reported (2, 11, 16, 22, 26), which indicate the paramagnetic nature of the oxidized complexes in contrast to the diamagnetism of the reduced forms. Studies at various temperatures indicate that the paramagnetic compounds follow Ciu ie s law closely and each possesses a permanent magnetic moment of about 1.7 Bohr magnetons, indicative of the presence of one unpaired electron. 

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