The effect of 1,3,5-trinitrobenzene on 1H nuclear magnetic resonance and electron paramagnetic resonance spectra of some cobalt(II) porphyrins

Abstract

The e.p.r. spectra of Co^II mesoporphyrin IX dimethyl ester and Co^II aetioporphyrin I, as frozen solutions in chloroform, are weak and suggest extensive association of the Co^II porphyrins. The presence in solution of 1,3,5-trinitrobenzene gives rise to much more intense resonances, with different g- and A-values-the ¹H n.m.r. spectra at 299 K of the Co^II porphyrins are assigned and it is found that the chemical shifts are increased by the addition of trinitrobenzene, presumably owing to the formation of the Co^II porphyrin-trinitrobenzene molecular complexes and the concomitant reduction in Co^II porphyrin association. The paramagnetic shifts are assumed to be due mainly to the dipolar contribution and the shifts calculated by use of parameters derived from the e.p.r. spectra agree well with those observed.