Field- and temperature-dependent 57Fe Mössbauer and high-frequency EPR (HFEPR) spectra were recorded for Fe-doped Zn4 (1,4-benzenedicarboxylate)3 (Fe-MOF-5). When measured under an Ar atmosphere, the data revealed a behavior consistent with that expected for low symmetry quasi-tetrahedral ferrous ions. In the presence of N2, however, the temperature dependence becomes exaggerated and the spectra cannot be fitted to a single species. A fluctuating electric field gradient at the Fe nuclei best explains these data and suggests dynamic structural distortions induced by weak interactions with N2. The combined analysis of the field-dependent Mössbauer and HF EPR data recorded for the dinitrogen-evacuated samples provided us with the zero-field splitting of the quintet ground state of the iron(II) ions. The computational investigation of these spectroscopic parameters allowed us to establish the electronic structure of the iron sites and to rationalize, in part, the observed flexibility of the Fe-MOF-5 SBUs. This direct evidence of dynamic behavior at MOF open metal sites is relevant for the use of MOF SBUs in catalysis, gas separation, and other applications that invoke similar phenomena.

Dynamic structural flexibility of Fe-MOF-5 evidenced by field-dependent Moessbauer and HFEPR

256th National Meeting (2018)

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