Direct Comparison of the Magnetic and Electronic Properties of Samarocene and Ytterbocene Terpyridine Complexes

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• 作者：Jacqueline M. Veauthier ; Eric J. Schelter ; Christin N. Carlson ; Brian L. Scott ; Ryan E. Da Re ; J. D. Thompson ; Jaqueline L. Kiplinger ; David E. Morris ; Kevin D. John
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：July 7, 2008
• 年：2008
• 卷：47
• 期：13
• 页码：5841 - 5849
• 全文大小：373K
• 年卷期：v.47,no.13(July 7, 2008)
• ISSN：1520-510X

文摘

A new complex, Cp*₂Sm(tpy) (1, where Cp* = C₅Me₅, tpy = 2,2′:6′,2′′-terpyridine) and its one-electron oxidized congener [Cp*₂Sm(tpy)]PF₆ ([1]⁺) have been synthesized and characterized with the aim of comparing their electronic and magnetic behavior to the known ytterbium analogues: Cp*₂Yb(tpy) (2) and [Cp*₂Yb(tpy)]OTf ([2]⁺). These new samarium complexes have been characterized using single-crystal X-ray diffraction, ¹H NMR spectroscopy, cyclic voltammetry, optical spectroscopy, and bulk magnetic susceptibility measurements. All data for 1 indicate a Sm(III)−tpy• ⁻[(4f)⁵−(π*)¹] ground-state electronic configuration similar to that found previously for 2 [(4f)¹³−(π*)¹]. Structural comparisons reveal that there are no significant changes in the overall geometries associated with the neutral and cationic samarium and ytterbium congeners aside from those anticipated based upon the lanthanide contraction. The redox potentials for the divalent Cp*₂Ln(THF)_n precursors (E_1/2(Sm²⁺) = −2.12 V, E_1/2(Yb²⁺) = −1.48 V) are consistent with established trends, the redox potentials (metal-based reduction and ligand-based oxidation) for 1 are nearly identical to those for 2. The correlation in the optical spectra of 1 and 2 is excellent, as expected for this ligand−radical based electronic structural assignment, but there does appear to be a red-shift (~400 cm⁻¹) in all of the bands of 1 relative to those of 2 that suggests a slightly greater stabilization of the π* level(s) in the samarium(III) complex compared to that in the ytterbium(III) complex. Similar spectroscopic overlap is observed for the monocationic complexes [1]⁺ and [2]⁺. Bulk magnetic susceptibility measurements for 1 reveal significantly different behavior than that of 2 due to differences in the electronic-state structure of the two metal ions. The implications of these differences in magnetic behavior are discussed.