TY - JOUR
T1 - A structurally-characterized peroxomanganese(IV) porphyrin from reversible O2 binding within a metal-organic framework
AU - Gallagher, Audrey T.
AU - Lee, Jung Yoon
AU - Kathiresan, Venkatesan
AU - Anderson, John S.
AU - Hoffman, Brian M.
AU - Harris, T. David
N1 - Funding Information:
Research in the Harris laboratory was funded by the U. S. Army Research Office (W911NF-14-1-0168 and W911NF-15-1-0331), the American Chemical Society Petroleum Research Fund (56081-DNI3), and Northwestern University. Research in the Hoffman laboratory was funded by the National Institutes of Health National Institute of General Medical Sciences (GM 111097). A. T. G. is supported primarily by the National Science Foundation through the Graduate Research Fellowship Program. We thank Dr C. Malliakas for assistance in modeling the X-ray diffraction data, Dr L. Liu for assistance in collecting powder X-ray diffraction data, Dr A. Marts for assistance in collecting initial EPR spectra, and Mr M. S. Fataah, Dr J. P. S. Walsh, and Dr A. Sharma for helpful discussions.
Publisher Copyright:
This journal is © The Royal Society of Chemistry. 2018.
PY - 2018
Y1 - 2018
N2 - The role of peroxometal species as reactive intermediates in myriad biological processes has motivated the synthesis and study of analogous molecular model complexes. Peroxomanganese(iv) porphyrin complexes are of particular interest, owing to their potential ability to form from reversible O2 binding, yet have been exceedingly difficult to isolate and characterize in molecular form. Alternatively, immobilization of metalloporphyrin sites within a metal-organic framework (MOF) can enable the study of interactions between low-coordinate metal centers and gaseous substrates, without interference from bimolecular reactions and axial ligation by solvent molecules. Here, we employ this approach to isolate the first rigorously four-coordinate manganese(ii) porphyrin complex and examine its reactivity with O2 using infrared spectroscopy, single-crystal X-ray diffraction, EPR spectroscopy, and O2 adsorption analysis. X-ray diffraction experiments reveal for the first time a peroxomanganese(iv) porphyrin species, which exhibits a side-on, η2 binding mode. Infrared and EPR spectroscopic data confirm the formulation of a peroxomanganese(iv) electronic structure, and show that O2 binding is reversible at ambient temperature, in contrast to what has been observed in molecular form. Finally, O2 gas adsorption measurements are employed to quantify the enthalpy of O2 binding as hads =-49.6(8) kJ mol-1. This enthalpy is considerably higher than in the corresponding Fe-and Co-based MOFs, and is found to increase with increasing reductive capacity of the MII/III redox couple.
AB - The role of peroxometal species as reactive intermediates in myriad biological processes has motivated the synthesis and study of analogous molecular model complexes. Peroxomanganese(iv) porphyrin complexes are of particular interest, owing to their potential ability to form from reversible O2 binding, yet have been exceedingly difficult to isolate and characterize in molecular form. Alternatively, immobilization of metalloporphyrin sites within a metal-organic framework (MOF) can enable the study of interactions between low-coordinate metal centers and gaseous substrates, without interference from bimolecular reactions and axial ligation by solvent molecules. Here, we employ this approach to isolate the first rigorously four-coordinate manganese(ii) porphyrin complex and examine its reactivity with O2 using infrared spectroscopy, single-crystal X-ray diffraction, EPR spectroscopy, and O2 adsorption analysis. X-ray diffraction experiments reveal for the first time a peroxomanganese(iv) porphyrin species, which exhibits a side-on, η2 binding mode. Infrared and EPR spectroscopic data confirm the formulation of a peroxomanganese(iv) electronic structure, and show that O2 binding is reversible at ambient temperature, in contrast to what has been observed in molecular form. Finally, O2 gas adsorption measurements are employed to quantify the enthalpy of O2 binding as hads =-49.6(8) kJ mol-1. This enthalpy is considerably higher than in the corresponding Fe-and Co-based MOFs, and is found to increase with increasing reductive capacity of the MII/III redox couple.
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U2 - 10.1039/c7sc03739b
DO - 10.1039/c7sc03739b
M3 - Article
C2 - 29675204
AN - SCOPUS:85041741499
VL - 9
SP - 1596
EP - 1603
JO - Chemical Science
JF - Chemical Science
SN - 2041-6520
IS - 6
ER -