Department of Chemical Engineering, University of California , Davis, California 95616, United States.
Department of Chemistry, Chemical Theory Center, and Supercomputing Institute, University of Minnesota , Minneapolis, Minnesota 55455-0431, United States.
J Am Chem Soc. 2016 Nov 23;138(46):15189-15196. doi: 10.1021/jacs.6b08273. Epub 2016 Nov 11.
Some metal organic frameworks (MOFs) incorporate nodes that are nanoscale metal oxides, and the hydroxy-containing functional groups on them provide opportunities for introducing catalytic sites with precisely defined structures. Investigations have been done to understand the structures of these groups on nodes and node vacancies, because, in prospect, atomic-scale modulation of the composition, areal density, and/or siting of the groups would open up possibilities for exquisite tuning of the siting and performance of subsequently anchored catalytic units (e.g., single metal ions, pairs of metal ions, or well-defined metal-ion-containing clusters). We have combined infrared (IR) spectroscopy and density functional theory (DFT) to demonstrate tuning of these sites, namely, hydrogen-bonded OH/OH groups on the Zr nodes of the MOFs UiO-66 and NU-1000 via the intermediacy of node methoxy (or ethoxy) groups formed from methanol (or ethanol). Methoxy (or ethoxy) groups on node vacancy sites are converted to a structure incorporating one vacant Zr site and one terminal OH group per face by reaction with water. Our results highlight how the combination of DFT and IR spectroscopy facilitates the determination of the identity and chemistry of the functional groups on MOF node vacancies and defect sites.
一些金属有机骨架（MOFs）包含纳米级金属氧化物的节点，而其含羟基的官能团为引入具有精确结构的催化位点提供了机会。已经进行了研究来了解这些节点和节点空位上的基团的结构，因为在未来，对组成、面密度和/或基团定位的原子尺度调制将为随后锚定的催化单元的定位和性能提供了极好的微调可能性（例如，单个金属离子、金属离子对或明确定义的含金属离子的簇）。我们结合了红外（IR）光谱和密度泛函理论（DFT）来证明这些位点的调谐，即在 MOFs UiO-66 和 NU-1000 的 Zr 节点上的氢键 OH/OH 基团通过甲醇（或乙醇）形成的节点甲氧基（或乙氧基）基团的中间态来进行。通过与水反应，节点空位上的甲氧基（或乙氧基）基团转化为每个面具有一个空位 Zr 位和一个末端 OH 基团的结构。我们的结果强调了 DFT 和 IR 光谱的结合如何促进对 MOF 节点空位和缺陷位点上的官能团的身份和化学性质的确定。
