Metal organic frameworks (MOFs) offer a promising platform for adsorption-based applications such as heterogeneous catalysis since their intrinsic porosity and tunable architecture allows gas/substrate selectivity and the incorporation of strategically placed reaction sites and other synergistic characteristics. Synthetic strides in developing new frameworks with these properties have, in some cases, far outpaced the progress in advancing the fundamental understanding of their adsorption-based processes and reaction mechanisms. Consequently, there are often significant ambiguities in the structure/function relationships that give rise to their utility. In this work we use a targeted set of vibrational, optical, and X-ray spectroscopy methods to make those connections by producing molecular level understanding of metal organic framework behavior. Specifically, a series of iron porphyrin-based MOFs is investigated upon post-synthetic treatment with both reducing and non-reducing guest molecule environments. These modified MOF environments serve to model potential intermediate species that may arise along catalytic pathways. Fe K-edge X-ray absorption and Kb mainline emission spectroscopy measurements reveal the local coordination geometry, oxidation and spin state changes experienced by the pore-facing Fe sites upon interaction with axially coordinating species. Analysis and fitting of these data confirm the binding patterns predicted by space filling models of the structurally constrained pore environments. These results, which are further support by UV-vis diffuse reflectance and resonance Raman spectroscopy data, provide new insights on the potential utility (and perhaps limitations) of metalloporphyrin-based MOFs as catalysts.

Probing framework-restricted metal axial ligation and spin state patterns in iron-porphyrin-based metal–organic framework catalysts

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.