Electronic Effects in Transition Metal Porphyrins. 10. Effect of Ortho Substituents on the Temperature Dependence of the NMR Spectra of a Series of Spin-Admixed Perchloratoiron(III) Tetrakis(2,

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• 作者：Marlys J. M. Nesset ; Sheng Cai ; Tatjana Kh. Shokhireva ; Nikolai V. Shokhirev ; Simone E. Jacobson ; K. Jayaraj ; Avram Gold ; and F. Ann Walker
• 刊名：Inorganic Chemistry
• 出版年：2000
• 出版时间：February 7, 2000
• 年：2000
• 卷：39
• 期：3
• 页码：532 - 540
• 全文大小：140K
• 年卷期：v.39,no.3(February 7, 2000)
• ISSN：1520-510X

文摘

The perchloratoiron(III) complexes of a series of 2,6-disubstituted tetraphenylporphyrin ligands, where the 2,6-phenyl substituents were -H, -F, -Cl, -Br, or -OMe, as well as two 2,4,6-phenyl-substituted complexes,where the substituents were -Me and -OMe, have been investigated as a function of temperature by ¹H NMRspectroscopy. Curvature in the 1/T dependence was evident in most cases. Forced linear extrapolation of thetemperature dependence observed over the range of the study yielded Curie plots that include negative slopeswith very large positive 1/T intercepts (Cl ~ Br > Me > H) to negative slope with near zero intercept (tri-OMe)to positive slope with very large negative intercept (F, di-OMe). The NMR results were combined with EPRspectroscopic data and curve-fitting procedures based on an expanded Curie law to arrive at a consistent overviewof the variety of temperature-dependence behaviors observed. This overview relies upon the premise that, inaddition to the ground state observed by EPR spectroscopy, one (or more) thermally accessible excited state(s)are populated to varying degrees over the temperature range of the NMR measurements. If only one excited stateis considered, the analysis is consistent with the ground state being a largely intermediate-spin state (S = ³/₂) forthe majority of the complexes but a largely high-spin state (S = ⁵/₂) for ((2,6-F₂)₄TPP)FeOClO₃ and((2,6-(OMe)₂)₄TPP)FeOClO₃.