Characterization of iron(III)porphyrin-hydroxo complexes in organic media through UV-Vis and EPR spectroscopies

The interaction of OH- with Fe(TPP)(+), Fe(TDCPP)(+), Fe(TMP)(+) and Fe(TFP P)(+) in 1,2-dichloroethane was studied by titrating FeP solutions with ali quots of a solution of tetrabutylammonium hydroxide in acetonitrile. The nu mber of OH- ions (n) coordinated to the FeP and the stability constants (be ta(n)) for the FeP-OH- complexes were calculated from UV-Vis absorbance dat a and iron spin states were determined through EPR spectroscopy, Fe(TMP) () forms a high-spin mono-hydroxo complex, while Fe(TPP)I and Fe(TDCPP)(+) f orm high-spin bis-hydroxo complexes. To our knowledge, this is the first ti me that the formation of bis-hydroxo complexes from Fe(TPP) (+) has been re ported, and this was possible because the studies were carried out in basic organic media, In this same medium, Fe-III-Fe-II reduction upon OH- additi on to Fe(TFPP) (+) was observed, without concomitant formation of the mu-ox o dimeric species [Fe(TFPP)](2)O. (C) 1999 Elsevier Science Inc, All rights reserved.