Nonheme oxoiron(IV) complexes can serve as synthons for generating heterobimetallic oxo-bridged dimetal complexes by reaction with divalent metal complexes. The formation of Fe III –O–Cr III and Fe III –O–Mn III complexes is described herein. The latter complexes may serve as models for the Fe III –X–Mn III active sites of an emerging class of Fe/Mn enzymes represented by the Class 1c ribonucleotide reductase from Chlamydia trachomatis and the R2-like ligand-binding oxidase (R2lox) found in Mycobacterium tuberculosis. These synthetic complexes have been characterized by UV–Vis, resonance Raman, and X-ray absorption spectroscopy, as well as electrospray mass spectrometry. The Fe III –O–Cr III complexes exhibit a three-band UV–Vis pattern that differs from the simpler features associated with Fe III –O–Fe III complexes. The positions of these features are modulated by the nature of the supporting polydentate ligand on the iron center, and their bands intensify dramatically in two examples upon the binding of an axial cyanate or thiocyanate ligand trans to the oxo bridge. In contrast, the Fe III –O–Mn III complexes resemble Fe III –O–Fe III complexes more closely. Resonance Raman characterization of the Fe III –O–M III complexes reveals an 18 O-sensitive vibration in the range of 760–890 cm −1 . This feature has been assigned to the asymmetric Fe III –O–M III stretching mode and correlates reasonably with the Fe–O bond distance determined by EXAFS analysis. The likely binding of an acetate as a bridging ligand to the Fe III –O–Mn III complex 12 lays the foundation for further efforts to model the heterobimetallic active sites of Fe/Mn enzymes.
Bibliographical noteFunding Information:
This work was supported by the National Institutes of Health (Grant GM-38767 to L.Q.). XAS data were collected at the Stanford Synchrotron Radiation Lightsource, which is supported by the U.S. DOE under Contract No. DE-AC02-76SF00515. Use of Beamline 7?3 is supported by the DOE Office of Biological and Environmental Research and the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393).
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- EXAFS analysis
- Heterobimetallic Fe–O–M complexes
- Oxoiron(IV) complexes
- Resonance Raman spectroscopy
- Ribonucleotide reductase