A detailed magnetic resonance investigation of the Fe(III), Ru(III), and Os(III) complexes with 2,2'bipyridyl and 1,10-phenanthroline has been carried out with the purpose of obtaining an accurate estimate of the dipolar contribution to the observed shifts, to establish, if possible, trends in and delocalization in this series of metal ion complexes and to compare our results for these t2g5 systems with the previously reported nickel(II) complexes with the same ligand. We find a large dipolar contribution to the shift which cannot be neglected and, as a result, show that the conclusions of a previous study of the Fe(III) complex are basically incorrect. Significantly, too, we find that the mechanisms of spin delocalization are radically different in the iron(III) and nickel(II) complexes and a model to account for this is proposed. Finally, we are able to say that Ru(III) exhibits a significantly greater degree of ir delocalization than either Fe(III) or Os(III) and that delocalization appears most important
Results of a detailed magnetic resonance investigation of iron group complexes of the form Mm(S-S)3"-(M = Fe, Ru, Os; S-S = bidentate sulfur donor ligand) are reported. The apparently near-isotropic g values of these complexes, in contrast to those of most other t2g5 complexes, are explained in terms of a consistent model of the bonding which requires a large low symmetry distortion both geometric and electronic in origin. This conclusion, contrary to that reached in previous epr studies, is supported by analysis of the hyperfine coupling arising from 10,Ru. It is found that the extensive metal-ligand covalent interaction reduces the spin-orbit coupling constant of Ru(III) to about 40% of its free-ion value and that the hyperfine coupling originates from both the usual indirect or polarization mechanism as well as a direct mechanism. Difficulties which arise from a purely 2T2 model are considered, and their effect on interpretation of the data is discussed. It is concluded that, when properly applied, the simple crystal field model will qualitatively yield the correct results, but, in the limit of large distortion from octahedral symmetry, the quantitative results of this treatment are of dubious value.
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