A five-coordinate heme dioxygen adduct isolated within a metal-organic framework.
The porphyrinic metal-organic framework (MOF) PCN-224 is metalated with Fe(II) to yield a 4-coordinate ferrous heme-containing compound. The heme center binds O2 at -78 °C to give a 5-coordinate heme-O2 complex. For the first time, this elusive species is structurally characterized, revealing an Fe(III) center coordinated to superoxide via an end-on, η(1) linkage. Mössbauer spectroscopy supports the structural observations and indicates the presence of a low-spin electronic configuration for Fe(III). Finally, variable-temperature O2 adsorption data enable quantification of the Fe-O2 interaction, providing a binding enthalpy of -34(4) kJ/mol. This value is nearly half of that observed for comparable 6-coordinate, imidazole-bound heme-O2 complexes, a difference that further illustrates the importance of axial ligands in biological heme-mediated O2 transport and storage. These results demonstrate the ability of a MOF, by virtue of its rigid solid-state structure, to enable isolation and thorough characterization of a species that can only be observed transiently in molecular form.
Department of Chemistry, Northwestern University , Evanston, Illinois 60208-3113, United States.
John S
JS
Anderson
Audrey T
AT
Gallagher
Jarad A
JA
Mason
T David
TD
Harris
D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry*
D005296:Ferrous Compounds; D010100:Oxygen