Dioxygen binding at a four-coordinate cobaltous porphyrin site in a metal-organic framework: structural, EPR, and O-2 adsorption analysis

作者：Gallagher Audrey T^*; Kelty Margaret L; Park Jesse G; Anderson John S; Mason Jarad A; Walsh James P S; Collins Shenell L; Harris T David

来源：Inorganic Chemistry Frontiers, 2016, 3(4): 536-540.

DOI：10.1039/c5qi00275c

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 metalorganic 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 (O2(-center dot)) ligand. Moreover, O2 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 O2 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.

• 出版日期2016
• 单位西北大学