| Autor: |
Firth FCN; Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom., Gaultois MW; Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, United Kingdom., Wu Y; Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, United Kingdom., Stratford JM; School of Chemistry, University of Birmingham, Birmingham B15 2TT, United Kingdom., Keeble DS; Diamond Light Source, Harwell Campus, Didcot OX11 0DE, United Kingdom., Grey CP; Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom., Cliffe MJ; School of Chemistry, University of Nottingham, Nottingham NG7 2RD, United Kingdom. |
| Abstrakt: |
The structures of Zr and Hf metal-organic frameworks (MOFs) are very sensitive to small changes in synthetic conditions. One key difference affecting the structure of UiO MOF phases is the shape and nuclearity of Zr or Hf metal clusters acting as nodes in the framework; although these clusters are crucial, their evolution during MOF synthesis is not fully understood. In this paper, we explore the nature of Hf metal clusters that form in different reaction solutions, including in a mixture of DMF, formic acid, and water. We show that the choice of solvent and reaction temperature in UiO MOF syntheses determines the cluster identity and hence the MOF structure. Using in situ X-ray pair distribution function measurements, we demonstrate that the evolution of different Hf cluster species can be tracked during UiO MOF synthesis, from solution stages to the full crystalline framework, and use our understanding to propose a formation mechanism for the hcp UiO-66(Hf) MOF, in which first the metal clusters aggregate from the M 6 cluster (as in fcu UiO-66) to the hcp -characteristic M 12 double cluster and, following this, the crystalline hcp framework forms. These insights pave the way toward rationally designing syntheses of as-yet unknown MOF structures, via tuning the synthesis conditions to select different cluster species. |
