Analysis of isotropic 1H and 13C NMR shifts of low-spin FeIII complexes: Tetracyano (1,2-ethanediamine) ferrate (III) and tetracyano (N,N'-dimethyl-1,2-ethanediamine) ferrate (III).
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概要
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<SUP>1</SUP>H NMR spectra of low-spin d<SUP>5</SUP> complexes, [Fe<SUP>III</SUP>(CN)<SUB>4</SUB>(en)]<SUP>−</SUP> and [Fe<SUP>III</SUP>(CN)<SUB>4</SUB>(<I>s</I>-Me<SUB>2</SUB>en)]<SUP>−</SUP> (en=1,2-ethanediamine, <I>s</I>-Me<SUB>2</SUB>en=<I>N</I>,<I>N</I>′-dimethyl-1,2-ethanediamine), were measured at 185–323 K. These complexes showed a non-Curie behavior. The spin states of the complexes were determined by an analysis of the <I>g</I> values from the ESR spectrum of a polycrystalline sample of [Fe<SUP>III</SUP>(CN)<SUB>4</SUB>(en)]<SUP>−</SUP> measured at liquid-helium temperatures. The isotropic shifts for the <SUP>1</SUP>H and <SUP>13</SUP>C nuclei, δ<SUP>iso</SUP>, were separated into Fermi contact shifts, δ<SUP>con</SUP>, and dipolar shifts, δ<SUP>dip</SUP> and the strong dependence of δ<SUP>iso</SUP> on the location of ligand nuclei was found to be due to the different δ<SUP>con</SUP> as well as δ<SUP>dip</SUP>. A combination of information concerning ESR and NMR enabled the assignment of the <I>g</I> values obtained from a polycrystalline sample, i.e. <I>g<SUB>xx</SUB></I>=3.15, <I>g<SUB>yy</SUB></I>=1.99, and <I>g<SUB>zz</SUB></I>=0.82, and determination of spin-orbit coupling constant, ζ=160 cm<SUP>−1</SUP>.
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