Comparison of the Temperature and Location Dependence of 1H and 13C NMR Shifts between Saturated 1,3- and 1,2-Diamines Coordinated to Low-Spin Tetracyanoferrate(III).
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The temperature dependence of the <SUP>1</SUP>H NMR for low-spin iron(III) complexes, [Fe<SUP>III</SUP>(CN)<SUB>4</SUB>(1,3-diamine)]<SUP>−</SUP>, with 1,3-propanediamine, (2<I>R</I>,4<I>S</I>)-2,4-pentanediamine, and (2<I>R</I>,4<I>S</I>)-2,4-pentanediamine were measured at 323–183 K. The coordinated amine segment, Fe–N(H<SUB>N</SUB>)<SUB>2</SUB>-C(H<SUB>α</SUB>)<SUB>2</SUB>–C(H<SUB>β</SUB>)<SUB>2</SUB>, resonated in the following magnetic field regions at 323–183 K: H<SUB>α</SUB><SUP>ax</SUP>, 7.2–20.5; H<SUB>β</SUB><SUP>ax</SUP>, 10.8–35.0; H<SUB>β</SUB><SUP>eq</SUP>, 23.9–65.7; H<SUB>β</SUB><SUP>methyl</SUP>, 1.8–9.9 ppm. All of the <SUP>1</SUP>H signals moved in the downfield direction with a decrease in the temperature, and exhibited a non-Curie behavior. The H<SUB>N</SUB> shifts at 300 K were 110–279 ppm. The temperature and location dependence of the isotropic shift (δ<SUP>iso</SUP>) for the <SUP>1</SUP>H and <SUP>13</SUP>C nuclei were accounted for by the combination of Fermi contact and dipolar contributions. The Fermi constants and spin populations were estimated for the <SUP>1</SUP>H and <SUP>13</SUP>C nuclei. Not only the spin polarization mechanism, but also a direct mechanism, were suggested for spin propagation from the Fe<SUP>III</SUP> to the respective atoms.
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