The study of cobalt porphyrin interactions with O_(2)is important owing largely to its relevance to biological heme-mediated O_(2)transport and storage.The immobilization of a metalloporphyrin site in a metal-organic ...The study of cobalt porphyrin interactions with O_(2)is important owing largely to its relevance to biological heme-mediated O_(2)transport and storage.The immobilization of a metalloporphyrin site in a metal-organic framework(MOF)enables the study of these interactions without interference from solution effects such as bimolecular reactions,axial ligation,and solvent/solute interactions involving the porphyrin ligand.Here,we investigate the reaction of O_(2)with the four-coordinate cobaltous porphyrin complex in the MOF PCN-224Co.Single-crystal X-ray diffraction and electron paramagnetic resonance(EPR)spectroscopy of the oxygenated form,PCN-224CoO_(2)reveals a five-coordinate low-spin Co^(III)center coordinated to an S=1/2 superoxo(O_(2)^(−)•)ligand.Moreover,O_(2)adsorption measurements on PCN-224Co reveal two distinct binding sites with adsorption enthalpies of h_(ads)=−15.2(6)and−10.2(3)kJ mol^(−1).The former binding event is ascribed to ligation of O_(2)at the open Co site,and the obtained value is considerably lower than those observed for cobalt porphyrin units in substituted proteins and model complexes that feature axial ligands.These results provide the first structurally-characterized five-coordinate Co–O_(2)species,further highlight the importance of axial ligation in biological O_(2)transport and storage,and demonstrate the ability of a MOF to enable isolation and study of a species that is highly unstable in molecular form.展开更多
基金funded by the U.S.Army Research Office through agreement numbers W911NF-14-1-0168,W911NF-15-1-0119,and W911NF-15-1-0331the U.S.Air Force Office of Scientific Research through agreement number FA9550-14-1-0274+4 种基金the Institute for Sustainability and Energy at Northwestern,and Northwestern Universitysupported primarily by the National Science Foundation through the Graduate Research Fellowship Programsupported primarily by the Chemistry of Life Processes through a Lambert Fellowshipsupported by the Northwestern University International Institute for Nanotechnologysupported primarily by the National Science Foundation under NSF Award Number EEC-1359004.
文摘The study of cobalt porphyrin interactions with O_(2)is important owing largely to its relevance to biological heme-mediated O_(2)transport and storage.The immobilization of a metalloporphyrin site in a metal-organic framework(MOF)enables the study of these interactions without interference from solution effects such as bimolecular reactions,axial ligation,and solvent/solute interactions involving the porphyrin ligand.Here,we investigate the reaction of O_(2)with the four-coordinate cobaltous porphyrin complex in the MOF PCN-224Co.Single-crystal X-ray diffraction and electron paramagnetic resonance(EPR)spectroscopy of the oxygenated form,PCN-224CoO_(2)reveals a five-coordinate low-spin Co^(III)center coordinated to an S=1/2 superoxo(O_(2)^(−)•)ligand.Moreover,O_(2)adsorption measurements on PCN-224Co reveal two distinct binding sites with adsorption enthalpies of h_(ads)=−15.2(6)and−10.2(3)kJ mol^(−1).The former binding event is ascribed to ligation of O_(2)at the open Co site,and the obtained value is considerably lower than those observed for cobalt porphyrin units in substituted proteins and model complexes that feature axial ligands.These results provide the first structurally-characterized five-coordinate Co–O_(2)species,further highlight the importance of axial ligation in biological O_(2)transport and storage,and demonstrate the ability of a MOF to enable isolation and study of a species that is highly unstable in molecular form.
