Department of Chemistry, University of Minnesota , Minneapolis, Minnesota 55455-0431, United States.
Chemical Theory Center and Minnesota Supercomputing Institute, University of Minnesota , Minneapolis, Minnesota 55455, United States.
ACS Appl Mater Interfaces. 2017 Nov 15;9(45):39342-39346. doi: 10.1021/acsami.7b11348. Epub 2017 Nov 1.
NU-1000 is a robust, mesoporous metal-organic framework (MOF) with hexazirconium nodes ([ZrOH], referred to as oxo-Zr nodes) that can be synthesized by combining a solution of ZrOCl·8HO and a benzoic acid modulator in N,N-dimethylformamide with a solution of linker (1,3,6,8-tetrakis(p-benzoic acid)pyrene, referred to as HTBAPy) and by aging at an elevated temperature. Typically, the resulting crystals are primarily composed of NU-1000 domains that crystallize with a more dense phase that shares structural similarity with NU-901, which is an MOF composed of the same linker molecules and nodes. Density differences between the two polymorphs arise from the differences in the node orientation: in NU-1000, the oxo-Zr nodes rotate 120° from node to node, whereas in NU-901, all nodes are aligned in parallel. Considering this structural difference leads to the hypothesis that changing the modulator from benzoic acid to a larger and more rigid biphenyl-4-carboxylic acid might lead to a stronger steric interaction between the modulator coordinating on the oxo-Zr node and misaligned nodes or linkers in the large pore and inhibit the growth of the more dense NU-901-like material, resulting in phase-pure NU-1000. Side-by-side reactions comparing the products of synthesis using benzoic acid or biphenyl-4-carboxylic acid as a modulator produce structurally heterogeneous crystals and phase-pure NU-1000 crystals. It can be concluded that the larger and more rigid biphenyl-4-carboxylate inhibits the incorporation of nodes with an alignment parallel to the neighboring nodes already residing in the crystal.
NU-1000 是一种结构坚固的介孔金属有机骨架（MOF），由六核锆节点（[ZrOH]，称为氧桥锆节点）组成，可通过将 ZrOCl·8HO 和苯甲酸调节剂在 N，N-二甲基甲酰胺中的溶液与链接剂（1,3,6,8-四（对苯二甲酸）芘，称为 HTBAPy）的溶液混合，并在高温下老化来合成。通常，所得晶体主要由 NU-1000 畴组成，这些畴结晶形成更密集的相，与 NU-901 具有结构相似性，NU-901 是一种由相同链接分子和节点组成的 MOF。两种多晶型物之间的密度差异源于节点取向的差异：在 NU-1000 中，氧桥锆节点在节点之间旋转 120°，而在 NU-901 中，所有节点都平行排列。考虑到这种结构差异，提出了一个假设，即改变调节剂从苯甲酸到更大更刚性的联苯-4-羧酸可能会导致调节剂与错位节点或大孔中的链接之间的空间相互作用更强，从而抑制更密集的 NU-901 样物质的生长，导致相纯的 NU-1000。使用苯甲酸或联苯-4-羧酸作为调节剂的合成产物的并排反应产生结构不均匀的晶体和相纯的 NU-1000 晶体。可以得出结论，较大且刚性更强的联苯-4-羧酸抑制了与已经存在于晶体中的相邻节点平行排列的节点的掺入。
