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The Chemistry of Nucleation: In Situ Pair Distribution Function Analysis of Secondary Building Units During UiO-66 MOF Formation |
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| Authors: | Dr Hui Xu Sanna Sommer Nils Lau Nyborg Broge Prof Dr Junkuo Gao Prof Dr Bo Brummerstedt Iversen |
| Institution: | 1. Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, 8000 Aarhus, Denmark
College of Materials Science and Engineering, China Jiliang University, Hangzhou, 310018 P.R. China These authors have equal contributed equally to this work.;2. Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, 8000 Aarhus, Denmark These authors have equal contributed equally to this work.;3. Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, 8000 Aarhus, Denmark;4. College of Materials and Textiles, Zhejiang Sci-Tech University, Hangzhou, 310018 P.R. China |
| Abstract: | The concept of secondary building units (SBUs) is central to all science on metal-organic frameworks (MOFs), and they are widely used to design new MOF materials. However, the presence of SBUs during MOF formation remains controversial, and the formation mechanism of MOFs remains unclear, due to limited information about the evolution of prenucleation cluster structures. Here in situ pair distribution function (PDF) analysis was used to probe UiO-66 formation under solvothermal conditions. The expected SBU—a hexanuclear zirconium cluster—is present in the metal salt precursor solution. Addition of organic ligands results in a disordered structure with correlations up to 23 Å, resembling crystalline UiO-66. Heating leads to fast cluster aggregation, and further growth and ordering results in the crystalline product. Thus, SBUs are present already at room temperature and act as building blocks for MOF formation. The proposed formation steps provide insight for further development of MOF synthesis. |
| Keywords: | in situ PDF metal–organic frameworks nucleation secondary building units UiO-66 |