Solution NMR Studies of Iron(II) Spin-Crossover Complexes
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- 作者：Birgit Weber ; F. Ann Walker
- 刊名：Inorganic Chemistry
- 出版年：2007
- 出版时间：August 6, 2007
- 年：2007
- 卷：46
- 期：16
- 页码：6794 - 6803
- 全文大小：185K
- 年卷期：v.46,no.16(August 6, 2007)
- ISSN：1520-510X
文摘
The 1H NMR spectra of a series of mono- and dinuclear pyridine complexes [FeL1(R1/R2)(py)2] and [Fe2L2(R1/R2)(py)4] have been investigated in a mixed toluene-d8/pyridine-d5 solution. The equatorial tetradentade Schiff baselike ligands L1(R1/R2) and L2(R1/R2) with a N2O22- coordination sphere for each metal center have been obtainedby condensation of a substituted malonodialdehyde (R1/R2 are Me/COOEt, Me/COMe, or OEt/COOEt) witho-phenylenediamine (L1(R1/R2)) or 1,2,4,5-tetraaminobenzene (L2(R1/R2)). The 1H NMR resonances were assignedby comparison of differently substituted complexes in combination with a line-width comparison. The 1H NMR shiftsfrom 188 to 358 K show a strong influence of the spin state of the iron center. The behavior of the pure high-spiniron(II) complexes is close to ideal Curie behavior. Analysis of the resonance shifts of the spin-transition complexescan be used for determining the high-spin mole fraction of the complex in solution at different temperatures. Magneticsusceptibility measurements in solution using the Evans method were made for all six complexes. Significantdifferences between the spin-transition behavior of the complexes in solution of those in the solid state were found.However, the plots of 
eff as a function of temperature obtained using the Evans method and those obtained byinterpretation of the NMR shifts were virtually identical. The isotropic shifts of protons in the complexes proved tobe suitable tools for following a spin transition in solution. Comparison of the eff plots of the mono- and dinuclearcomplexes in solution reveals slight differences between the steepness of the curves that may be attributable tocooperative interactions between the metal centers in the case of the dinuclear complexes.
eff as a function of temperature obtained using the Evans method and those obtained byinterpretation of the NMR shifts were virtually identical. The isotropic shifts of protons in the complexes proved tobe suitable tools for following a spin transition in solution. Comparison of the eff plots of the mono- and dinuclearcomplexes in solution reveals slight differences between the steepness of the curves that may be attributable tocooperative interactions between the metal centers in the case of the dinuclear complexes.