Exposing the inadequacy of redox formalisms by resolving redox inequivalence within isovalent clusters.

Autor: Bartholomew AK; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138., Teesdale JJ; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138., Hernández Sánchez R; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138., Malbrecht BJ; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138., Juda CE; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138., Ménard G; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138., Bu W; ChemMatCARS, The University of Chicago, Argonne, IL 60439., Iovan DA; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138., Mikhailine AA; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138., Zheng SL; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138., Sarangi R; Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025-07015., Wang SG; ChemMatCARS, The University of Chicago, Argonne, IL 60439., Chen YS; ChemMatCARS, The University of Chicago, Argonne, IL 60439., Betley TA; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138; betley@chemistry.harvard.edu.
Jazyk: angličtina
Zdroj: Proceedings of the National Academy of Sciences of the United States of America [Proc Natl Acad Sci U S A] 2019 Aug 06; Vol. 116 (32), pp. 15836-15841. Date of Electronic Publication: 2019 Jul 19.
DOI: 10.1073/pnas.1907699116
Abstrakt: In this report we examine a family of trinuclear iron complexes by multiple-wavelength, anomalous diffraction (MAD) to explore the redox load distribution within cluster materials by the free refinement of atomic scattering factors. Several effects were explored that can impact atomic scattering factors within clusters, including 1) metal atom primary coordination sphere, 2) M-M bonding, and 3) redox delocalization in formally mixed-valent species. Complexes were investigated which vary from highly symmetric to fully asymmetric by 57 Fe Mössbauer and X-ray diffraction to explore the relationship between MAD-derived data and the data available from these widely used characterization techniques. The compounds examined include the all-ferrous clusters [ n Bu 4 N][( tbs L)Fe 3 (μ 3 -Cl)] (1) ([ tbs L] 6- = [1,3,5-C 6 H 9 (NC 6 H 4 - o -NSi t BuMe 2 ) 3 ] 6- ]), ( tbs L)Fe 3 (py) (2), [K(C 222 )] 2 [( tbs L)Fe 3 (μ 3 -NPh)] (4) (C 222 = 2,2,2-cryptand), and the mixed-valent ( tbs L)Fe 3 (μ 3 -NPh) (3). Redox delocalization in mixed-valent 3 was explored with cyclic voltammetry (CV), zero-field 57 Fe Mössbauer, near-infrared (NIR) spectroscopy, and X-ray crystallography techniques. We find that the MAD results show an excellent correspondence to 57 Fe Mössbauer data; yet also can distinguish between subtle changes in local coordination geometries where Mössbauer cannot. Differences within aggregate oxidation levels are evident by systematic shifts of scattering factor envelopes to increasingly higher energies. However, distinguishing local oxidation levels in iso- or mixed-valent materials can be dramatically obscured by the degree of covalent intracore bonding. MAD-derived atomic scattering factor data emphasize in-edge features that are often difficult to analyze by X-ray absorption near edge spectroscopy (XANES). Thus, relative oxidation levels within the cluster were most reliably ascertained from comparing the entire envelope of the atomic scattering factor data.
Competing Interests: The authors declare no conflict of interest.
Databáze: MEDLINE
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