| Research Abstract |
Hyoperfine (hf) splittings due to the 57 Fe nucleus (I=1/2) have been obsarved for the first time from frozen-solution ESR measurements on low-spin Fe(III) heme complexes, Fe(TPP)(OMe)_2^-, (1), and Fe(TPP)(SET)(MrOH), (2), where TPP is tetraphenylporhine dianion. Remakable differnces in the hf splitting (A_<(i)> ) values of the gi sbsotption peaks (i=X, Y, Z) are founs between the two low-spin specices: For (1), A_<(X)>=6.1,A_<(Y)>=15.6, and A(_<(Z)>=8.6 G, while, for (2), A (_x)= 18.1, A_<(Y)>=3.6, and A_<(Z)>=3.4 G. These results are analyzed within the framework of a low-symmetry cystal field model. Equations are devied which relate the A_<(i)> values with the angular orientation of low-symmetry filed. A numerical analysis aha shown that the axes of rhombic component field in (1) and (2) are rofated about the home normal by 39.3 and 6.9゜, respectively, suggesting that the two species have distinctly different orientations of the axial ligand(s). The analysis of the A(i) data has also enabled us to determine the relative orientations of g and hf tensors, the sign of g tensor determinant,and the lowsymmetry crystal field pastameters.
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