Raman Signature of the Fe2O2 “Diamond” Core

We report the resonance Raman (RR) spectra of iron complexes containing the Fe2(μ-O)2 core. Frozen CH3CN solutions of the FeIIIFeIV intermediate [Fe2(μ-O)2L2](ClO4)3 (where L = TPA, 5-Me3-TPA, 5-Me2-TPA, 5-MeTPA, 5-Et3-TPA, or 3-Me3-TPA) show numerous resonance-enhanced vibrations, and among these,...

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Bibliographic Details
Published in:Journal of the American Chemical Society 1998-02, Vol.120 (5), p.955-962
Main Authors: Wilkinson, Elizabeth C, Dong, Yanhong, Zang, Yan, Fujii, Hiroshi, Fraczkiewicz, Robert, Fraczkiewicz, Grazyna, Czernuszewicz, Roman S, Que, Lawrence
Format: Article
Language:English
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Summary:We report the resonance Raman (RR) spectra of iron complexes containing the Fe2(μ-O)2 core. Frozen CH3CN solutions of the FeIIIFeIV intermediate [Fe2(μ-O)2L2](ClO4)3 (where L = TPA, 5-Me3-TPA, 5-Me2-TPA, 5-MeTPA, 5-Et3-TPA, or 3-Me3-TPA) show numerous resonance-enhanced vibrations, and among these, an oxygen-isotope-sensitive vibration around 667 cm-1 that shifts ca. 30 cm-1 when the samples are allowed to exchange with 18OH2, and whose Raman shift does not vary with methyl substitution of the TPA ligand. Spectra of iron-isotope-substituted samples of [Fe2(μ-O)2(L)2](ClO4)3 (54Fe and 57Fe for L = TPA, and 54Fe and 58Fe for L = 5-Me3-TPA) show that this vibration is also iron-isotope-sensitive. These isotopic data taken together strongly suggest that this vibration involves motion of the Fe2(μ-O)2 core that is isolated from motions of the ligand. A frozen CH3CN solution of the diiron(III) complex [Fe2(μ-O)2(6-Me3-TPA)2](ClO4)2 shows one intense resonance-enhanced vibration at 692 cm-1 that shifts −30 cm-1 with 18O labeling. Normal coordinate analysis of the Fe2(μ-O)2 core in [Fe2(μ-O)2(5-Me3-TPA)2](ClO4)3 supports the assignment of the Fermi doublet centered around 666.2 cm-1 as an A1 vibration of this core. Furthermore, we propose that this unique feature found in the region between 650 and 700 cm-1 is indicative of a diamond core structure and is the Raman signature of an iron cluster containing this core.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja973220u