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DOI: 10.1039/A907113J (Paper) Reference Section for: Chem. Commun., 1999, 2339-2340

X-Ray absorption spectroscopic studies of the Cr(IV) 2-ethyl-2-hydroxybutanoato(1–) complex†

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Aviva Levina, Peter A. Lay and Garry J. Foran

Abstract

The first X-ray absorption spectrum of the rare Cr(IV) oxidation state has been obtained for the complex with the ehbaH ligand [ehbaH = 2-ethyl-2-hydroxybutanoate(1–)] in frozen aqueous solution (14 K), showing that at pH = 3.5 and in a large excess of the ligand, the predominant form of Cr(IV) is the five-coordinate oxo complex, [CrIVO- (ehbaH)2]0.

References

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  5. Abbreviations: ehba = 2-ethyl-2-hydroxybutanoate(2–); XAS = X-ray absorption spectra; XANES = X-ray absorption near-edge structure; XAFS = X-ray absorption fine structure; SS = single scattering; and MS = multiple scattering.
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  11. Electronic supplementary information (ESI) is available (http://www.rsc.org/suppdata/cc/1999/2339/), including: (i) tables showing the parameters of XAS experiments, the conditions, constraints and restraints applied to the XAFS fittings, the results of SS and MS XAFS calculations and the contributions of different scattering paths into the calculated MS XAFS; and (ii) figures showing typical kinetic data of Cr(IV) decomposition; XANES spectra of fresh and exposed Cr(IV) samples, the results of SS XAFS simulations for Cr(V/IV/III)–ehba and the structure of I refined by MS XAFS (11 pp.).
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  22. The Cr–O bond lengths in the Cr(III)–ehba complex, determined from SS XAFS calculations (1.94 Å),11 are in agreement with the proposed structure of this complex.13 The Cr–O bond lengths in [CrIII(OH2)6]3+(determined from MS XAFS calculations) are 1.97 Å(H. Sakane, A. Muñoz-Páez, S. Díaz-Moreno, J. M. Martínez, R. R. Pappalardo and E. S. Marcos, J. Am. Chem. Soc., 1998, 120, 10 397) Search PubMed.
  23. The different Cr–O bond lengths in Na[CrVO(ehba)2] involving the carboxylato and alkoxo moieties (1.90 and 1.80 Å, respectively)10 are not distinguished by SS XAFS when k≤ 11 Å–1 since the resolution in bond lengths is 0.15 Å.17 These data are in agreement with the results of SS and MS XAFS calculations for solid Na[CrVO(ehba)2](T. Maschmeyer, G. Barr-David, P. A. Lay and A. F. Masters, to be submitted).
  24. The V–O(alcohol) bond length in NH4[VIV(ehba)(ehbaH)] is 1.95 Å.3 The presence of unusually long (> 2 Å) Cr–O bonds in I is consistent with the ease of loss of one ehbaH ligand in solution.1,2.